Unencrypted MT

Hi list! As described in Nico Golde's talk at 29c3, mobile operators can deactivate encryption on MT SMSes. To check if a MT is encrypted I've started 'mobile' with GSMTAP, and I've sent an sms to the mobile. Encryption seems to be requested by the network. Now the question is: how can I be sure that encryption is always activated? Should I exaustively send messages to the mobile in order to look for unecrypted messages? Or is there some other way? People who give stats about MNO do exaustive tests, or simply generate a bunch of events and campute stats on those results? Thanks for your answers/opinions. Dario.