SPV C550 GPRS reconnection problem...

I have an ex-Orange SPVC550 on T-mobile Web'n'Walk Pro. Until recently
it was fine.

However in the past couple of weeks the GPRS has been very flaky. After
power up GPRS connections are fine.

After a few minutes inactivity however it wont transfer any data even
though the Windows icon still shows connected.

Disconnecting and reconnecting under Windows causes it to hang at the
dialog box saying it is registering on the network.

Connections on the phone have the same effect and it wont make voice
calls either.

Selecting the "disconnect GPRS" option has no effect.

The only thing that seems to work is power cycling or switching flight
mode on and off which is a real PITA. It the reregisters on the network
and it works for a while.

Any ideas? I haven't installed any software which could have affected it
IIRC. Might a cold reset, reflashing with Orange firmware help?

The only other variable is I've changed location slightly from Towyn to
Prestatyn, North Wales, a 5 bar signal in both locations. I did notice
however that on the odd visit to Bangor I also got a 5 bar signal and
almost no GPRS at all.

Steve.