Smartphone TMobile MDA III (HTC Kaiser) connection problem

[-gem-]

I've had one of these for a while now and mostly it works a treat. I'm having problems surfing the web on it though.

I can connect to the internet using Virgin's setup for 'GPRS/3G' (HSDPA), and it transfers data ok, cos that's the only way it can feed the GPS software that needs it. The browser works too, when I connect to the internet in a wifi hotspot. But when I use the browser otherwise it makes the HSDPA connection ok, which shows up as connected, but no web page loads. I even tried it in Opera, nothing happens. Any ideas gratefully appreciated.