VoIP over IPsec

["Charles Youse" <cyouse () register com>]

Hello again,

I've heard a lot of encouraging things on this list in response to my previous inquiries about VoIP - hoping you can 
help me out again.

In order to cut costs in our telecom budget I'm toying with the idea of replacing a lot of our inter-office leased 
lines with VPN connections over the public Internet.  (I've got a lot of experience doing this in major production 
environments so I'm aware of the gotchas in this scenario.)  My general method is to create IPsec-encrypted GRE tunnels 
between sites and then treat them as true virtual circuits; i.e., I run OSPF over the tunnel and exchange dynamic 
routing information, blah-de-blah.

Assume for the moment that latency and bandwidth are not an issue; e.g., any two points that will be exchanging voice 
data will both have transit from the same provider with an aggressive SLA.

Does anyone have any experience running VoIP over such tunnels?  Is there a technical reason why this solution is not 
feasible?  Are Cisco routers not happy doing VoIP/IPsec/GRE in concert?

Thanks as always,
C.