proxy.atl.broadvoice.com supports G726.32, G729 and G723.
Quality is VERY good with the 726 and is below average with the other two. (the 726 implementation means I can finally use 3-way conferencing from my underpowered Russian 105 kbs upstream line that won't handle two G711 streams).
What it does not support at the moment is Call Manager. When registered to ATL, calls dialed via web-based CM will return "resource unavailable".
And, as an update to
this thread, NYC proxy (and maybe some others) will allow you to go 726/729/723 for both incoming and outgoing calls, including CallManager-initiated ones.