You unbox an NB-IoT sensor, pop in a spare data SIM from the drawer, and the device never finds a network. In most cases the card is the problem: an NB-IoT SIM card is not an ordinary phone SIM but a card on a plan where the network operator has explicitly enabled NB-IoT access. On top of that, the SIM slot size, the APN from your provider and the frequency bands of device and network have to match.
So the short answer is this: you need an IoT or M2M SIM with NB-IoT enabled, on a network that actually broadcasts NB-IoT where the device will be installed, in the format your hardware accepts. The examples below use the Dragino CPL03-NB contact sensor and the RAKwireless RAK5860 WisBlock cellular module.
Does a normal SIM card work with NB-IoT?
Usually not. NB-IoT runs on the operators’ LTE infrastructure, but it is a separate radio standard (LTE Cat NB1 and NB2) that has to be enabled on the network side. A smartphone plan normally does not include that entitlement. Put such a card into an NB-IoT sensor and the network rejects the attach, or the sensor searches until it gives up. Dragino’s guide for its -NB models puts it plainly: a SIM that doesn’t explicitly support NB-IoT normally won’t work.
Also separate NB-IoT from LTE-M. The RAK5860 with its Quectel BG77 handles both LTE-M (Cat M1) and NB-IoT (Cat NB2). The Dragino CPL03-NB with the Quectel BC660K-GL, by contrast, is NB-IoT only. A plan that only enables LTE-M won’t help the CPL03-NB, even if both cards say “IoT” on the packaging. Ask the provider which technology, networks and countries your plan covers.
An active PIN can also get in the way: a sensor has no way to enter one, which is why IoT SIMs usually ship with the PIN disabled. If yours has a PIN, turn it off in a phone first. Before inserting the card, write down its ICCID, the card number printed on it. You’ll need it to check activation status in the provider’s portal.
Which UK networks offer NB-IoT SIM cards?
In the UK, NB-IoT is not available from every network, and no single network covers the whole country on one technology. Vodafone is the operator most closely associated with NB-IoT and runs it on Band 20 (800 MHz). EE/BT has NB-IoT on Band 3 (1800 MHz), but without LTE-M. O2 has gone the other way: it offers LTE-M on Band 20 and, according to a 2024 device-maker network guide, no NB-IoT at all. That guide rated Vodafone and EE NB-IoT coverage as reasonable but with gaps, and advised a multi-network SIM for near-national coverage.
Rollouts change, so check each operator’s coverage checker for your exact address. Those maps describe outdoor coverage; NB-IoT reaches deeper into buildings than standard LTE, but a meter pit or metal cabinet can still be too much. Only a test with the real device and SIM at the mounting point is reliable.
Many IoT connectivity providers resell access to one or more of these networks on their own cards, so what matters is which network a card may use for NB-IoT. If you deploy in Germany instead, all three operators there, Telekom, Vodafone and O2, run NB-IoT networks; Telekom states IoT availability well above 95 percent, and Vodafone reported around 95 percent NB-IoT coverage in Q3 2024.
On the hardware side, most European NB-IoT networks use Band 8 (900 MHz) and Band 20 (800 MHz), and Dragino recommends that band combination for Europe. The CPL03-NB supports both, plus Band 3, among 17 bands from B1 to B85.
How much does an NB-IoT SIM cost?
NB-IoT plans are built differently from phone contracts. Three models are common: one-off bundles, where you prepay a fixed amount of data for a long term; a recurring monthly or yearly fee per SIM with a small included allowance; and pooled plans, where many SIMs share one data pool. The network operators themselves also sell IoT and M2M plans, usually with a one-time or yearly fee rather than a classic monthly contract. Prices, data allowances and terms change regularly, so always compare current offers before you commit.
The real costs sit elsewhere: activation fees, minimum terms, roaming surcharges, a static IP address, or a private APN with a VPN link. For a handful of devices, a one-off bundle is usually simplest; for large fleets, a pooled plan with a management portal makes more sense.
Also find out what happens when the data runs out: is the SIM throttled, blocked, or automatically topped up at a charge? A sensor misconfigured to report every two minutes instead of hourly burns through a bundle thirty times faster. Many providers show usage per ICCID in their portal and let you set limits or alerts.
How to set the NB-IoT APN
The APN (Access Point Name) defines which gateway in the mobile network your data goes through. Your SIM provider supplies it, along with any username, password and the IP type, such as IPv4, IPv6 or Non-IP. Don’t guess it or copy one from a forum post. A wrong APN typically means the device registers on the network but never gets a data connection. Some networks assign a default APN when none is set.
Where you enter it depends on the device. On the Dragino CPL03-NB and the other Dragino -NB models, you set it with the vendor-specific command AT+APN=your.apn, sent over the serial configuration interface. Dragino also documents AT+QCGDEFCONT, which stores the PDN settings in the module so they are used during the attach. AT+CFG then confirms the entry.
On the RAK5860, you talk to the Quectel BG77 directly using the Quectel AT command set, over UART from the WisBlock Core in the finished build, or over the module’s Micro-USB port while testing. The standard route is AT+CGDCONT=1,”IP”,”your.apn”, which defines PDP context 1 with your APN; AT+CGDCONT? reads the stored contexts back. RAKwireless’s quick start guide also shows AT+QICSGP for the module’s internal TCP/IP stack.
A private APN that links devices to your company network over a VPN only helps if your server is reachable that way; otherwise the sensor stays silent although SIM and network work fine.
Does an NB-IoT SIM work abroad (roaming)?
Sometimes, but far less reliably than ordinary mobile service. NB-IoT roaming requires the home network and the foreign network to have an agreement for this specific technology. A regular LTE roaming deal is not enough. Coverage of such agreements is patchier than for LTE-M or regular 4G.
Battery life matters too. The power-saving features PSM and eDRX, which let an NB-IoT sensor run for years on one battery, also have to be supported by the visited network. Without them the modem stays awake longer, and a sensor like the CPL03-NB with its 8,500 mAh battery drains faster than the datasheet suggests. Ask for a list of countries and networks where your SIM may use NB-IoT, including any PSM or eDRX limits.
The hardware is less of a concern: with 17 bands, the CPL03-NB covers the common frequencies worldwide. But if you used AT+QBAND to lock it to your home network’s bands, such as 8 and 20 in Germany, you have to lift that lock before deploying elsewhere, or the sensor will never find a network on a different band. To see whether a device is actually roaming, check its registration status: on Quectel modules, AT+CEREG? returns 5 for roaming and 1 for the home network.
Nano SIM, eSIM or MFF2: which SIM format for NB-IoT?
The format decides whether a card fits your device and whether you can switch providers later. Here is how they compare.
| Format | Size | Replaceable | Typical use |
|---|---|---|---|
| Mini SIM (2FF) | 25 × 15 mm | yes | older routers and modems |
| Micro SIM (3FF) | 15 × 12 mm | yes | older modules and gateways |
| Nano SIM (4FF) | 12.3 × 8.8 mm | yes | current sensors and modules such as the CPL03-NB and RAK5860 |
| MFF2 (soldered) | 6 × 5 mm | no | production devices facing vibration, moisture, wide temperature ranges |
| eSIM (eUICC) | chip or card | profile swapped remotely | devices that may need to change provider later |
The CPL03-NB has a nano SIM slot. The RAK5860 has a nano SIM holder on its back and, according to the manufacturer, is also offered with an eSIM option. Dragino advises powering the sensor off before inserting the card and minding the orientation; a card that isn’t seated properly later looks like a network fault in the portal.
MFF2 is a SIM chip soldered directly onto the board. It copes with vibration and moisture better than a card holder, but it can’t be swapped. With an eSIM (eUICC), the network profile is downloaded remotely and can be changed. For outdoor installations, make sure the SIM is rated for the device’s temperature range; the CPL03-NB is specified for -40 to +85 °C, and industrial-grade IoT SIMs are built for that kind of range.
How much data does an NB-IoT sensor use?
Less than you’d expect, if the protocol fits. A contact sensor like the CPL03-NB reports status, open duration and event counts, which is only a few dozen bytes of payload. For one hourly UDP report: about 50 bytes of payload plus 28 bytes of IP and UDP headers gives roughly 80 bytes per message. That is just under 2 KB a day, about 58 KB a month, and well under one megabyte a year.
The picture changes when the protocol adds overhead. The CPL03-NB can send via MQTT, MQTTs, TCP or UDP, and Dragino’s -NB series also supports CoAP. If the sensor opens a new TCP connection with an MQTT login for every report, a few hundred bytes up to around one kilobyte per message adds up quickly. With TLS encryption (MQTTs) and a fresh connection each time, the certificate handshake adds several kilobytes more. At 5 KB per hourly report you land at about 3.6 MB a month and just over 40 MB a year. Over ten years that is more than 400 MB, which would nearly use up a small one-off bundle.
According to Dragino, MQTT also uses more power than UDP or CoAP. Build in headroom: after a coverage gap, the CPL03-NB uploads the events it logged in the meantime, weak signal can trigger retransmissions, and firmware updates over the cellular network, if you use them, come on top. As a rule of thumb, double your calculated usage.
NB-IoT SIM not registering: what to check
Work in a fixed order and change one thing at a time. Stage one: does the device detect the SIM? On a Quectel module like the BG77 on the RAK5860, AT+CPIN? should answer READY. AT+CIMI returns the IMSI, the subscriber identity whose first digits reveal the home network, and AT+QCCID returns the ICCID, which you compare with the printed number and the provider portal. If neither comes back, the card is seated wrong.
Stage two: is the SIM active and enabled for NB-IoT? The provider’s portal shows that. Stage three: is the device searching in the right mode? The BG77 supports LTE-M and NB-IoT; AT+QCFG=”iotopmode” sets whether it uses LTE-M only (0), NB-IoT only (1) or both (2). On the CPL03-NB, AT+QBAND? shows the band setting, so you can check whether an old band lock excludes your provider’s network.
Stage four: the registration itself. On the BG77, AT+CEREG? shows the registration status; 2 means it is still searching, and 3 means the network rejected the attach, which almost always points to a missing NB-IoT entitlement. On the CPL03-NB, the signal value tells you: according to Dragino, a value between 0 and 31 means a successful attach and 99 means failure. The network search runs for up to five minutes by default, and AT+CSQTIME lets you extend it. On the RAK5860, also check that the LTE and GNSS antennas sit on their correct IPEX connectors.
Stage five: if the device is registered but nothing arrives, the SIM is rarely to blame. Check the APN next, then the server address, port and protocol, on the CPL03-NB with AT+SERVADDR and AT+PRO. AT+CFG and AT+GETLOG collect what Dragino support needs.
Where can you buy NB-IoT sensors?
Before you pick a device, run through the questions above in order. Does the modem support NB-IoT or only LTE-M, and does that match your plan? Does it cover your network’s bands, such as Band 20 for Vodafone in the UK? Which SIM format does the slot take: nano SIM, eSIM or a soldered MFF2 chip? How do you set the APN, with a vendor command as on the CPL03-NB or with AT+CGDCONT as on the RAK5860? Which protocols are available, and how much data do they generate at your reporting interval? And finally, will you be able to switch networks later?
Only once the device and the NB-IoT SIM card match on all of these points is a test at the mounting site worth doing. If you’re looking for a suitable device, you’ll find our models in the NB-IoT category.
NB-IoT SIM Card FAQ
Do I need an M2M SIM for NB-IoT?
In practice, yes. What matters is not the label but that the plan enables NB-IoT access on the network, which IoT and M2M plans do and phone plans normally don’t. Get the NB-IoT activation confirmed before you buy.
Can I use an NB-IoT SIM card in my phone?
Not in any useful way. Most smartphones don’t support NB-IoT, and many NB-IoT plans don’t allow regular LTE, voice calls, or often even SMS. A phone is still handy for disabling the PIN.
Do NB-IoT SIM cards expire?
The card itself doesn’t, but the plan does. One-off bundles are valid for a fixed term, usually several years, or until the data is used up. Some providers also deactivate SIMs that stay unused for a long time, so check the terms of your plan.