First off I know that not everyone likes the 3 network and also this phone receives mixed reviews from what I could find, but anyway...
The ZTE 102 is all about affordability. You can make free Skype-to-Skype calls and chat for free with Windows Live Messenger. And it's easy to flick between applications with the switcher key.
It comes with a 2 megapixel camera and has an impressive battery life - so you can use all the 3G features for longer.
NO £10 topup required unlike argos
£8 cashback from quidco or topcashback which reduces this to £11.99
Don't use accessory voucher codes as they usually invalidate the cashback
UPDATE: It appears the ZTE F102 Black is no longer available, however the ZTE F102 Silver still is though!http://threestore.three.co.uk/PAYG/dealsummary.aspx?offercode=DSL0PP199