@scottalanmiller is right. The bottleneck is always the customer router. And not so much bandwidth as much as packets per second. Your dropbox sync is killing your phone calls 50 to 1 over bandwidth 99% of the time. Your $50 linksys router can't handle a million pps.
Most ISP's are little more than Broadsoft resellers with no interconnects in their local market. Even on the WISP side speeds are so good now that bundling voice isn't relevant.