The HTC G-1 has only been released for T-Mobile, but it sounds like you may have unlocked it to work on AT&T Mobility.
Assuming that you'd gotten your phone fully unlocked, Im guessing that your mobile email settings are incorrect to receive your email in a timely fashion. I would call the cell phone carrier's technical support line and walk through setting up the correct MMS/SMS/Email settings with them.
The number is 800-331-0500 for customer care, make sure you dial that from a landline number and not the G-1.

