Hiya,
Couple of things
1. Get an extension cord and move the cordless base station further away from the PC
2. Sell off your current PC speakers, and look for 'Magetically Shielded' speakers
The 'mobile' static usually occurs when the phone is communicating with the Base station or 'Cell Site' its currently sitting in. Happens every so often. If/when a call comes in, you can tell with an increase in intereference and the characteristic sound it makes if the mobile is close to some speakers or audio equipment connected to speakers.
I'm not 100% sure if all the 'computer speakers' you see in places like PC world are magentically shielded - I'd assume they are as they often sit close to PC monitors. You could *cough* buy some modest speakers from PC world, try em out and if they dont get interefered with keep em else take em back *cough*
Good luck!
Cheers, DtM! West London & Slough UK!