Amazing bit of kit and suffers no interference from either blue tooth or 2.4ghz wireless networks. This plugs into a windows XP system, supports your normal telephone line and also crystal clear Skype calls.
Skype to Sype is free and Skype out provides cheap world wide calls. I use one in my office in UK and another in spain thus never pay more than 2cents a minute... even mobiles are cheaper.
Skype software is free to download and use.
If you don't want a skype phone or use PC, I purchased a Binatone digital cordless which resolved interference from my wireless network