Hi Jun,
Without a doubt, I'd recommend flowroute since you're setting up your own voip server at your location.
Reasons I like flowroute:
0. There's some kind of [in]direct support to freeswitch. I don't know the exact politics of the support, though.
1. You can easily setup failover to a DID, SIP URI, or a host address. You may think this is standard for all VOIP providers, but places like vitality charge more per-min to do failover.
2. Support is super responsive and very knowledgeable
4. Free inums and you can forward to URI, DID, host
5. They just enabled cname support on incoming calls
6. Never had a service interuption
8. They supported calling inums before releasing inums. Some companies think of inmus as competition, but flowroute did not have that impression.
9. free calling to toll free numbers
10. Free test account with 25 cent credit. Sign up and make some calls. You won't be able to receive calls until you buy a DID, though. (that's expected)
What I would like improved at Flowroute:
0. Better DID search. As of now, you must select an area code, then a rate center to see all available numbers. There's no way to search for a string in their available list.
What I hope will be released at flowroute:
0. Public API with a very good userguide.
1. SMS support
My next favorite suggestion would be
voip.ms
Hope this helps!
happy new year,
jungleboogie