If you're finding that customers who did not expect you to offer VoIP service in the past would now like to order it from you, then this is a service you want to offer ASAP.

Deciding to outsource the service makes sense. You might, in the long term, develop the expertise to move the service in house. But if you're learning this business, consider the companies listed here.

Many VoIP providers do not allow ISPs to resell their service, but welcome agents and referrers. If you want to be a referral agent for a VoIP service, almost every VoIP service has an agent program. If you're small, one or more of these agent programs may make sense for you.

If you're only offering residential service, also consult the Good, Bad, and Ugly rankings at Broadband Reports.

Few VoIP services offer everything that those listed here provide: turnkey VoIP service that allows ISPs to obtain more monthly revenue (and profit!) from each existing customer.

As you narrow your choices further, be sure to check out the Quick Reference Chart.

360networks' VoIP360
Apps Communications
BandTel
CommPartners
Ensim Unify
Intelliverse
IPsmarx
Junction Networks
MegaPOP VoIP
Nuvio
SinglePipe
SysMaster
TeleMedium
VarPhonex by InPhonex
VoX Communications
VT White
ZCorum's VoiSelect
Zoom Technologies' VoIP ASAP