Some, yes you can but not with all. I say its open for debate. For example, you can flash a gsm phone over to a cdma network but you cant use a cdma to gsm network. You cant even use a cricket phone on metro or vise-versa, and they both are cdma. You can use any phone with a sim card on different networks that use sim cards but you need an unlock code. Simple mobile, which is a network of the t-mobile company does exactly that. They will unlock any sim card phone so you can use with their network. It all depends on the phone and what company you got it from. Hope this helps answer your question and if Im wrong anywhere, please go ahead and correct me, whoever finds where I may be wrong at.
