I've just done it today!
Went into CPW, showed them my completely knackerd Nokia.
I've got 5 months left of my contract with O2/CPW.
To buy out my contract would have cost me £141.03, CPW gave me £100, a brand new Samsung Tocco Lite touch screen on a £30 pm contract with 700 mins and 700 texts a month with T-Mobile.
So it actually cost me £41.03.
It'll do me