btw, in a T1, you probably wont get 24… because you need 1 D channel for call control (but true, you can have like 1 D channel for multiple T1’s).
T1 is 1.5Mbps Upload AND 1.5Mbps Download
the g711 itself encodes voice at 64kbps so 1.5*1024 / 64 = 24
And usually a conversation is two-way, but that just means you upload as much as you download… So it will just use both UL and DL.
As for SIP g711, bandwith usage depends on packet size:
5ms: payload: 40Bytes, Overhead: 54Bytes => 150.4 kbps
20ms: payload: 160Bytes, Overhead: 54Bytes => 85.6 kbps
That will always be more than voice T1
Your mistake is thinking ‘two way call down’ when actually it’s one way UP, one way DOWN