I'm with CPW and recently moved to an alternative tariff (some of you
might have noticed it in an earlier thread).

One of the things that came up was the lack of memory for text
messages on the sim cards we already had (about 4 years old) and new
sim cards were received a few days ago which should have kept the same
number etc.

The sim cards came up as unregistered at the time, but as the new
contract was only supposed to start today, I wasn't too concerned.

I tried one of the new sims again this evening, and again i'm getting
"unregistered sim".

I believe it's a new O2 3G sim (O2 markings) - does anyone know if i'm
missing something dumb like needing to rediscover the network or
something ? (i'm seeing all the 4 main operators, but trying to
connect to the O2 network from the options gets me nowhere)

Thanks in advance for any clues, short of me getting on the phone to
them again tomorrow :-}