vision phones vs. 2.5G WW phones will differ in this regard as noted by the previous poster...

if anyone had a 2.5G phone, they can get sms as long as their phone can receive sms's. they do get so many sms's free then you have to pay for more.

for vision phones it is different as you have to be provisioned on the network (have your username/pswd in the system). i usually send sms's (when i rarely do) to people on non vision phones which is how i know they don't have to have a sms-specific plan in place.