The RUT950 uses standard size SIM cards.
We recommend that you use the mobile broadband packages available from most network providers rather than use the unlimited data plans which are available for smartphones because these unlimited mobile internet plans are contractually only for use in smartphones. The mobile networks do monitor usage of their unlimited data plans and if they are being used in a device other than a smartphone then they will restrict access. They do this by checking the IMEI of the device.
If you need remote access to the Teltonika RUT950 4G Router then please bear in mind that the 4G Data SIM cards available directly from EE, Vodafone, O2 and 3Mobile (including the MVNO partners of these primary networks eg. Tesco, Virgin, Netwok ID, BT etc) willl only provide your connection with a PRIVATE IP Address so you will not be able to remotely connect to the router. This also means that you will not be able to use DYNDNS because the service provider has only given the 4G connection a PRIVATE IP address on their network.
As far as we are aware the only mobile network to provide a PUBLIC IP Address suitable for remote access / DYNDNS is 3mobile and that is only if you connect at 3G speeds using the APN of 3internet. 3mobile will not allocate a public IP address if you connect at 4G speeds and this service is not a contracted part of their service offering and due to availability it may not always be available and may be stopped at any time.
For remote access and monitoring applications where you need to connect to the router and use port forwarding to connect to your devices on the LAN we recommend a 4G Fixed IP Data SIM Card.