Go to "Settings > General > Network > Cellular Data Network" and enter the following settings:
Cellular Data
APN: internet.vistream.net
Username: WEB
Password: vistream
Visual Voicemail
APN: [empty]
Username: [empty]
Password: [empty]
MMS
APN: mms.vistream.net
Username: [empty]
Password: [empty]
MMSC:
http://172.30.66.40:20080
MMS Proxy: 172.031.043.021:8080
MMS Max Message Size: 307200
MMS UA Prof URL: [empty]