I cant say for sure about VZW, but AT&T will allow this I'm told, though you'll have to change the APN.
Originally Posted by Haswell1150
Keep in mind Verizon uses CDMA which attaches to the phone's ESN/IMEI, so swapping the SIM may not do any good (I tried this on Sprint a couple years back with a "world phone" that used a Sprint SIM and it wouldn't activate)
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