SIM is not changing network

If your SIM does not appear to be changing networks this can be for a number of reasons:

1. There is no alternative network at your location
2. It is the device that decides if it wants a different network.  The device tells the SIM to change network if it is not happy with the signal strength. Therefore, the device will keep the same network if it is happy with the local signal strength. 

Signal strength, change networks