Wirelessly posted (8800: BlackBerry8800/4.2.1 Profile/MIDP-2.0 Configuration/CLDC-1.1 VendorID/102)
1. If you have a bunch of friends/family you need instant access to, then I guess it would be.
2. I doubt it. PTT is at&t's version of it.
3. No idea. Probably based on cell number or IMEI.
4. I believe the cost is $19.99/mo.