[zAy0LfpBZLC8mAC]

I would be very surprised if any telco were using any sort of compression internally (other than G.711, obviously). 64 kb/s with RTP/IP framing overhead is about 100 kb/s, that's just not a lot of bandwidth anymore that it would be worth installing hardware to do de-/compression. Even a gigabit link can carry ~ 10000 such calls--that's a drop in the bucket compared to the internet needs of the many more than 10000 subscribers that you need to ever have 10000 concurrent calls (probably more in the range hundreds of gigabits, possibly terabits).