probably been done before but it can't hurt to repost in case someone missed it. It's not a bad deal if you are a light user. Basically you call chitter chatter, they send out a t-mobile sim and from there you can deal directly with T-Mobile. T-mobile will debit your account £10 each month but chitter chatter will credit you back the £4 on the same day.
Instead of unlimited data you can choose Unlimited Texts, Unlimited
Landline or Unlimited T-Mobile to T-Mobile calls