I just found out about this and thought it was great! The current (old?) 'Free Texts' O2 PAYG tariff was £10 topup for 300 txts, £20 for 500 and £30 for Unlimited texts, all with 1MB of free internet. You can now change tariff to the new 'Text & Web' tariff, which gives the same text benefits, but also with UNLIMITED internet.
However, it gets BETTER. Change Tariff before 31st Jan and your tariff will give you UNLIMITED TEXTS for £10-14 top-up and UNLIMITED TEXTS AND INTERNET for £15 topup! (The allowance counts for 1 calendar month after you top-up).
Great deal I think - considering what you have to pay for contracts with 'unlimited' data allowances and texts!
On top of this remember you can also get O2 treats, O2 Rewards and O2 Surprises with each top-up!
Just call 2202 from your O2 phone to find out more and change tariff!
FYI: 'unlimited' in this deal is 12,000 texts a month and 500MB data. (FYI: Orange 'unlimted' data allowance for iPhone is 750mb, so this is amazing for PAYG!)