Virtual Roaming Control 0.12
the author of this app says:
This app lets you to control which network operators your phone is allowed to connect to (roaming). You can select to allow your phone to connect to all network operators from your country or create a custom list of allowed networks operators.
You can decide to block the connection entirely (set airplane mode) or only the data connection (needs external free app APNdroid) when the phone tries to connect to not allowed operators
This app is specially useful for Mobile Virtual Network Operators (MVNO) that connect to several real network operators.
Please report any problems or suggestions to email@example.com.
Note1: This app only works in GSM phones.
Note2: It can not be installed in the SD as it requires a background service to be run.