Phone Calls Briefly Cut Out BB (Eircom Wireless)

Every time someone answers or makes a call it causes our wireless BB (Eircom) to stop working. It usually fixes itself after a few minutes but it's a bit of a nuisance. We did have a different problem a while back and they sent out a replacement router which is the one we're on at the minute. It worked fine initially.

I can't remember the model details as I'm not at home but I can check this evening - both were/are Netopia things. At the time, getting coherent tech support was like pulling teeth.

Any ideas if this is down the router or something else? One of the lights usually goes red when it happens. Thanks.