for a good fun phone a android is best and is more customizable then those proprietary in house operating systems ussually very slow and feature restricted.
here are two options for a quick no waiting android phone
1 Tesco has a startup android Advertised Sim free for about £50.00
2 Phones4U had a Huawei blaze my choice was on for the total price of £69.99 inc. £10.00 pre-activation top up you will lose the 10 pounds to the O2 sim but still worth it. forgot buy with debit card if with cash they will charge £20.00 top-up, if not ask the chap for a startup android phone for O2 ie compatible with giffgaff.
one online option if you are willing to wait.
3 online there are cheaper options for android phones which i can say if you are willing to wait for delivery is worth researching around, amazon.co.uk market place has not let me down yet for my cheap tech choices.
and adding the £10.00 goodybag to it for me was a good thing specially on long distance public transport journeys, I can go on the Internet without worrying about the usual costs, and not experience the slow way thaty my previous feature phones used data well i can say it was frustrating to say the least..
features for a goodybag for £10.00:
unlimited texts [for me no warnings or messages for over-using so far ]
unlimited internet [no tethering two devices together, for me using 1.1 GB no wanrings or other problems so far]
for more info go here ---> http://giffgaff.com/goodybags/10pound-facebook-goodybag
There has been a few users who have complained about beeing barred for over usage breaking T&C's, for me though not a issue so far.
updated for better more complete information!!!