With giffgaff your going to want to use a goodybag, th basic one costs £10 a month and gives you
250 minutes (any ntwork)
Unlimited texts
Internet (has rules but they havent been a problem for me)
I think you also get free calls to other giffgaff numbers, so I moved the wife over a well. Porting the number was easy, I just completed the online form, gave the date I wanted and it went according to plan. Another good point is hat its all PAYG so you can jump ship if anything better comes up. Network wise its all on O2.
There are also other bonuses for non goodbag users, inlcluding some free internet, fee calls and txts to other giggfaff users.
If you do want a sim click my link below and we each get £5 of credit
http://giffgaff.com/orders/affiliate/fenix