Price increases all around for UK prepaid

[Motel75]

Speaking for myself, it seems either Vodafone or T-Mobile is the best offer, probably Vodafone - mainly because of the free 60 international minutes with a 10 pound topup, and the fact that web browsing costs 50p a day (not GBP 1 with TMO) and the ubiquitous 0845 numbers, which many companies now use and I am forced to call a lot, are 25p with VF and 40p with TMO.

Unless Virgin suddenly starts to compete on price again, I do plan to switch from Virgin when I'm back in the UK in a couple of months (I'm on Virgin Direct Debit, which costs 35p to other networks - not good). Couple things I'm not clear about:

Can you port a number to an existing SIM? Or do you have to go to the official Vf/TMO shop with PAC code and get one there?

As far as expiration goes, Virgin claims you need a billable action every 180 days, but experience suggests it's really 365 or more (this has been a major reason for me to stick with VM). VF and TMO both require billable actions every 180 days. Is this correct, or is there more leeway?