Have seen the Samsung Galaxy Y which looks a nice little phone. It's sim free so can you please tell me as simply as poss exactly what I would need to do/buy to get it up and running as a pay as you go.
DD just turned 11 and has had an old Samsung Galaxy of mine for the past year without breaking/losing it, so for her birthday she got a new Samsung Galaxy S3 mini - bought it sim-free on Amazon, so just put her existing Tesco mobile sim in it, and that was that.
Depending on where you're getting it, it can be cheaper to buy phone with sim on a PAYG package, eg lots of options here, but if you've found a good deal on a sim-free phone, you just need to shop around for the best sim-only deal, depending on how much you think she's going to used it, whether you want her to have mobile data (DD doesn't - she can access wifi at home, but I don't really want her having mobile internet access generally), whether she's likely to go on massive texting sprees with friends etc.
If you think you're likely to top up by at least £5 a month, it's worth looking at GiffGaff which has some of the best deals around (but goodybags only last a month at a time). Tesco mobile also has some good deals, eg if you top up a certain amount, they triple it for a month.