Listen to the guys above.. I am not an apple guy whatsoever.. however google is still implying the Iphone 4s is possible to do as I have implied.. but no way I care to research it because apple I would just whip at a wall
.. but I have decided to have you consider another method altogether which can turn any phone into useable.
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How about just dont use the phone network at all puff_>>
Use the phone for wifi and get
Talkatone app (apple) and/or google voice and/or NetTalk app (android) and you can talk/text/etc all you want for free and have the internet too puff_>>
who needs a network when you can have "free" (based on wifi service you may or may not pay for)
-murph