Edgewater Edgemarc might be your answer (Score 1)

I used to work for a VoIP company, although on the IP side of things (so i'm no expert on the edgemarc), and we looked at using Edgemarc as our CPE for businesses. These devices can be statefully aware of active voip calls and when there is bandwidth contention, it can adjust the tcp windowing of your non-voip traffic which slows the remote host's transmission of data. it's a reactive solution and the edgemarcs aren't cheap, but businesses use them. don't hold me to it, but it might be worth checking out. i think they make a few SOHO models.