I'm fairly sure it was due to: allowing users to pay for Internet access, T-Mobile (and other WiFi providers) will allow some very specific pages to go through their access rules.
As such, though I couldn't find them, I'm sure that they must have had Google Maps somewhere in their open site perhaps by way of 'contact us', thus they're allowing the IPs that serve up the Google mapping content.
Equally, if I tried to visit http://maps.google.com it wouldn't allow me to access the page. However, searching maps directly in the Maps app would allow me to search.
Two things you might be asking yourself:
- If you've got the maps app, surely you can just visit it via edge, since it comes on the iPhone? Nope, I've, ::erhem:: tweaked my iPod Touch to give me maps and mail.
- Sadly, I've found this nice little hack doesn't work in the UK.
It would be great to know whether any other countries support this hack, if you happen to have an iPod Touch or iPhone and near a T-Mobile connection point!