You can change the technologies that the network will allow the device can connect to.
It is now possible to turn on and off different technologies at a network level per SIM. This will result in the device being denied if it tries to connect using a disabled technology.
What are the technology options?
2G/3G cannot be separated.
Guidelines for implementation.
We recommend testing this feature throughly before rolling out to devices that have been deployed. It is strongly recommended to disable technologies while the device is not online to avoid undefined behaviour. Disabling a technology while the a device is currently connected using the specific technology can in rare cases, to some extent, cause undefined behaviour - test it out to make sure this case is correctly handled in the firmware. In most cases the device will simply be 'kicked off' and can immediately start attaching to an available network.
Finally, the time to attach after updating the allowed technologies could potentially increase as the device can spend time trying to attach to technologies that are not allowed. This will only be the case the first time as the last known 'good' network is saved by the modem and subsequent connection attempts will use this information.
The modem has been observed to be attached on the GSM net (AT+CREG? +CREG x,5) even if all technologies are disabled.
Make sure this is correctly handled in the device firmware as the modem will not be able to activate a PDP context. If relying on CREG for registration status this can cause the device to end up in an unwanted state.