Re Denis Wolff's question (Broken modem connections, September, p136):

One possibility not mentioned may be that the phone is on the same line as his modem, assuming he has just "paralleled up" the lines. Some early model phones, particularly the Telecom ones with a membrane touch pad, poll the line every few minutes. When this happens, the modem connection will be dropped. Unplug the phone and no more worries.