Aluminium iMac connectivity issue

I have an aluminium iMac first revision and I have the aluminium bluetooth keyboard and wireless mighty mouse connected to it. However every so often the mouse will disconnect itself for 5-10 seconds then reconnect. This also happens with the keyboard, sometimes both disconnect at the same time and the mouse pointer lags on screen. Other times I have to switch the mouse on/off to get the mac to pick it up again. This has been happening since I first bought the iMac but thought it was just Leopard and an update would sort it out but this has not happened. Any ideas?

Also I tried to connect a bluetooth device, a Sony Ericsson W910i phone to transfer some photos/videos across to the iMac but the the phone would not connect to the iMac to even though I had registered the device on the mac and the iMac was set to discoverable. The phone says it has found the iMac but it will not let me transfer the photos/videos across and keeps saying "connection failed". I tried about 10 times and it failed everytime. I was in range as I was sitting right in front of the computer less than a metre away.

Could there be a problem with my bluetooth module?