Om writes about the fact that Vonage, CallVantage, et al, sell hardware that is service specific.
If you want to change services, you have to buy new hardware. (Not to mention, see about taking that VOIP number with you!) So, you offer VOIP, sell it as Open Standards. Sell is as Non Proprietary. BTW, Pulver has a good quote:
"As someone who has fought for open standards in VOIP, I think this trend
totally defeats the purpose. People are trying to differentiate their products
when they should be focusing on making it easier for consumers to use VOIP."