SMS is not supported by Nextel on these.
You can get incoming SMS's but it won't say who they came from. There is no integrated option to SMS out from a Nextel Blackberry, you'd have to use teleflip or email
and make sure everyone SMSing you knows to identify themselves.
We found this out the hard way when Tmobile users upgraded to Nextel phones.
BTW: I've tried using teleflip but the phone never the message.