AS it is happening by wired ethernet as well you can rule out a wireless problem being the cause.
What ISP? Is it AOL?
Try changing the MTU in the router to 1450 or 1400 (I think it's under WAN settings)
Do you have a microfilter on EVERYTHING all phones, faxes, answer machines, sky, is there an alarm linked to the phone?
Have you upgraded the router firmware?