OP states the wireless is disabled on the router.
More likely culprit is the power supply / wall wart for the router is electrically noisy.
Not easy to cure really as the router power supply is naturally somewhere near the phone line as a matter of course.
Does the same problem occur using a wired phone rather than your dect phone?
Edited by GeeTee (Tue 01-Mar-11 12:18:25)