T610 vs. Sony Vaio vs. XP - 692 error on dial up

OK, I've made (I think) some good progress on this, but the last bit
is escaping me...

When I use the Sony-Ericsson Dial-Up Networking wizard to create a
connection it all sets up fine, but when I use the connection, I get
error 692 everytime.

If I use Hyperterminal on COM5 I can kick off a connection no problem
- the number appears on my phone display as Calling... and the call
connects.

So why - if COM5 is happily working - am I getting the 692 (hardware
fault) error?

The devices are paired, COM5 is showing up everywhere as the right
port, and the phone has installed successfully as a modem within XP.

Next question - when are one of these manufacturers going to make this
a bit simpler? I work with these kind of comms problems daily and I've
found just getting the phone to work with Sony/XP bluetooth
exasperating...

Cheers

Rob