How to keep photon in gsm mode.

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http://forum.xda-developers.com – I m using photon on gsm network. I want to know is there any way.to keep the phone in gsm mode by default? It seems the phone goes back to cdma mode if its out of network for long duration. Can anyone help with build.prop edit? I'm currently using cm7 Sent from my DROID RAZR using Tapatalk 2 (HowTos)