What is the experience with this? SIP with no SBC.

It depends on the customer equipment. We typically use voip.ms trunks. They work just fine with no SBC on the astrisk based systems we install. They aren't so happy or easy to setup without an SBC on the Mitel/shoretel systems.

I have used this with the Samsung systems we have installed. It works quite well. Haven't really had a lot of issues. Do have a few customers that have a SBC with a ata behind it. Seems to work just as well. Although, doesn't seem to make much of a difference from the customers that I have without a SBC. So honestly I don't see much gain from it if you really don't need one.

Using SIP without an SBC isn't an issue. However, security is a little tricky without one. I like the SBC.s because you don't have to think about port forwarding to 5060. The router doesn't have to allow 5060 to the outside world.

Scott helped me get an old TA908 working with a couple SIP trunks, but because it sits behind my router, there are some NAT issues and as a result, the lines do not ring...I can call out all day though.