Hard resetting should have restored ALL settings to factory defaults (e.g., the settings it had when you first got it home and took it out of the box).
Here's something to try:
Go to settings and open up connections. Tap on "manage existing connections". Under the "Modem" tab your set up should show the Power Vision radio button checked and under number have "#777".
Tap on "edit". The fix box should read "Power Vision". The next box should read "Cellular Line".
Tap on "next" and confirm that the dialing number is #777.
Tap on "next" and confirm your user name. If it's not listed or you're not sure what it is you can log onto the Sprint website and get it. But it should be something like
xxxxx@sprintpcs.com.
Tap finish and exit it out of the connection menu all together.
Can you make and receive calls ok? Can you send and receive texts?
Let us know what's up.
late,
Coz