I have set up my gmail account through the my iPhone 5 "mail" feature. Recently, while I'm out using the 3G network I try to refresh my email and I get "Cannot Get Mail - No internet connection available" Any firm solutions?

I have set up my gmail account through the my iPhone 5 "mail" feature. Recently, while I'm out using the 3G network I try to refresh my email and I get "Cannot Get Mail - No internet connection available" I know the 3G is working because I can access other things. I've read a couple of forums on this already. Restarting my phone worked but it's only a temporary fix. Anybody know of any firm solutions?

Thanks for the help.