I used to get this when I first bought a 56k global modem
for my V50.  The problem was that my service provider
had not enabled my phone number/sim for fax/data.  Get
in touch with your network provider, they will sort it out.

The only frustrating thing for me was that I had to get my
bill provider to talk to my network provider, and that was
tricky.  The bills were coming from Vodafone when the
network provider was BT Cellnet/O2  I got the impression
they didn't like talking to one another.  Later when one of
them decided that I would be better off on a different
tarrif, they changed my tarrif without talking to me, and in
that change disabled fax/data again.  Great denial of service
attack that was a real challenge to bash the two together
and get it sorted out quickly, since I was on-call and on
the move.

Anyway, network provider, contact them, get the data tap
turned on.  (or fawcet if you're in the US)

Pete.