If you use Call Waiting, and another call comes in while you are on line, the warning bleep can cause modems to disconnect. Call waiting on a BT line can be switched off temporarily before connecting to the Net by using the code #43# and switched back on later with *43# (these need to be separate calls).

If you have just a single line for voice calls and Internet connection, the BT Answer 1571 scheme may be a better option - instead of interrupting you, this will intercept and record incoming calls. It has the advantage of being free. For details see: http://www.bt.com/answer.jsp

You will need to supply your phone number and customer number. You may also want to explore other discounts.