**You get unlimited data as long as you don't abuse your data connection.
Oh and if you are having trouble trying to get data/mms working on your cappy with ST, here are the APN settings.
1. Download APN Back up/ restore from the Play Store
Name: ST (or whatever you want)
Username: Not set
Password: Not set
Server: Not set
MMSC: http:// mmsc. cingular. com (no spaces)
MMSC proxy: 188.8.131.52
MMS port: 80
Authentication Type: Not set
APN type: default,supl,mms
APN protocol: IPv4
Bearer: Not specified
I use this with Froyo, Gingerbread, and ICS. It works perfectly!
Cheers and let me know if this helps you out.
ST ATT 4G LTE APNs