What's the point?
Pretty much everyone who wants a mobile phone already has one. Obviously you will get some stolen to be sold abroad, some stolen because they're in someone's handbag, and some pinched from kids by other kids. However the market for dodgy phones has collapsed. You can buy a basic pay & go phone with £10 airtime for less than £20 (the Motorola F3 Blue, as recommended at http://www.reghardware.co.uk/2007/03/29/review_motorola_motofone_f3/). This is new, comes from a shop and has a warranty (and obviously isn't stolen).
The same happened with knocked off computer memory. When SIMMs cost £30 or more per MB (just before Windows 95 was released) there was quite a lot of money to be made with corporate machines having up to 64 MB. However the collapse in price meant that it just wasn't worth it any more. You can now buy a 1 GB DIMM for less than £20, which is equivalent to 1 MB costing less than 2p.
Sometimes it's just basic economics that cuts crime, not yet another initiative from the Home Office.