I tested this last week with a standard Rezound, running 4.0.3, as OTA updated. I bought a pre-paid T-Mobile SIM (Easy-Free) card in Europe, and results are similar to what is already known:
* Used "LTE On/Off" app to switch function to GSM, signal level bars were observed
* On awaking, the phone displayed a message "SIM is from an unknown source. Emergency calls only."
* Occasionally lost signal bars and switched back to CDMA
* Could dial and receive voice calls, and receive text messages
* Could not send text messages
* No APNs were visible, and attempts to enter were unsuccessful, "Bearer" menu lacked GPRS setting, internet was not working
* Never observed less than 5-bars signal level
* Notification bar displayed a message "SIM card is full, please delete some messages."
Interestingly, T-Mobile texted me frequently with the pre-paid rates for local, incoming, MMS, and SMS. It was nice to have the warning. Rates rose drastically when the phone registered on AT&T and then T-Mobile back in the USA.
I'd say this wasn't entirely successful, but it filled part of the need.