This is a known issue . This is because mobile providers route all Internet requests through multiple static IP addresses. Handsets are terminals within their own internal network (and usually have an IP address of 10.nnn), and all traffic is routed through external proxies.
There is no other way than
- convince Google of AT&T proxy whitelisting
- convince AT&T to use more proxies
- vote with your feet to use a service provider that has more proxies.