Make sure that you have the correct APN settings.
Name: Public Mobile
APN: sp.mb.com
Proxy: Leave blank
Port: Leave blank
Username: Leave blank
Password: Leave blank
Server: Leave blank
MMSC: http://aliasredirect.net/proxy/mb/mmsc
MMSC proxy: 74.49.0.18
MMS port: 80
MCC: 302
MNC: 220
Authentication type: Leave blank
APN type: default,mms,agps,supl,fota,hipri
APN protocol: IPv4
APN roaming protocol: IPv4
Bearer: Unspecified
MVNO type: GID
MVNO value: 4D4F
Don't forget to save these settings and then select this APN as the active one.
