I blame both the ISP's and SIP carriers - but mostly the ISP's!
Here is Ontario we have two key players providing internet. Bell and Rogers - they both provide crap service in their own special ways.
1. Rogers cable likes to mess around with traffic shaping screwing with SIP/voip and p2p programs.
2. Bell has such old copper cabling for DSL they don't even have to try. When it rains major parts of the city impacted with degraded DSL services. Bell is not interested in repairing anything unless they have to.
SIP carriers have to rely on ISP's for good service so they can deliver their product. Unfortunately many of them do not invest in the proper equipment and good upper tier carriers to provide that good product.
Combine that with bad ISP service and you have a recipe for lousy SIP service!
I never have trusted SIP carriers and for the few clients that I regretfully setup with SIP crriers I will be removing in 2010!
Until we have excellent internet service and excellent SIP carriers i won't be going setting up anyone with SIP carriers. Good is not good enough for SIP carrier service.
Please note that I believe the future is SIP and VOIP protocols and I will these technologies in phones and gateways. I just won't be using over the internet. voip does not equal internet. it's voice over "internet protocol" - we are using the this in phones and gateways over standard analog/pri lines. We do not need to use the internet - its just the protocol!