Phone Calls disconnect broadband

[#1]

Any ideas why incoming (and probably outdoing) phone calls cause my wireless nroadband to drop out? Everything else works fine.
I have a normal BT line.

[#2]

Is it just the wireless that's dropping or is it the connection to the exchange?
Have you tried connecting to your router with a wire to see if the problem persists?
Are you using DECT phones? Sometimes DECT (digital cordless) phones interfere with wireless.  You could try changing the channel your wireless broadcasts on from your router's wireless set up and see if that makes any difference.

[#3]

The phone call continues so I assume the exchange connection is maintained and it is just the wireless that drops out. It is an old fashioned plug in phone.

[#4]

The phone and broadband are different signals down the same line.  Your router can loose synchronisation with the exchange (and you loose your connection) but the phone will still work.
Have you got a microfilter plugged into every socket where there is a phone attached (or a Sky box/answering machine etc.) as well as where you plug your router in?  Is the phone your using connected via a microfilter?