if you re due to upgrade and call them you can ask for:
12mth contract | 500min (mix & match)| 3000min 3to3 network | 2GB internet allowance - upgrade custromers only.
(Told them i was getting 500min with T-mobile for £7.50 on 1mth contract, which is true).
Was paying £10 for same deal after end of contract.
Also they will only offer you the same number of minutes you were on, ie.My 500min contract ended and they would only offer me the same number of minutes (ie 500) , i needed more but they wouldnt m- anyway cant have it all :).
Anyway probably useful to someone as it halved my yearly bill from £120 to £60 inc VAT.