I know of several firms that provide this type service besides Vontage. For a west coast specific solution, PM me and I will send you names to several independent telecom consultants in California who can provide specific recommendations.
Speaking in general terms, this type service can add value in several specific areas. However, a combined telephone and Internet access is probably the least of these.
1) PBX services to SOHO locations and non-technical locations.
2) Common exchange across multiple locations.
3) Ability to maintain office local calling for road warriors.
4) Ability to retain office “presense” for temporary remote work locations.
The continuing drops in circuit costs make the convergence aspect of IP telephony a decreasing factor in my opinion. The location independence aspects become the driving factor.