I need some help understanding bandwidth, I've always had difficulty keeping the units of bandwidth measurement straight.
Voice quality is directly impacted by the codec used. Default in CallManager is G7.11, which takes up 80Kb/s for each voice call. Does this mean that a 1.5/384 circuit (which translates to 1,572 Kbps/384 Kbps) will be able to support about 4 calls using G7.11? (384/80 = 4.7 calls, rounded down to 4 calls)
Does this also mean that a PRI, which will run at 1.5Mb/s up and down, which translates to 1572 Kb/s up and down will suport just under 20 calls without degradation?
Your calculation for ADSL is correct.
But, PRI (primary rate interface) is not a data circuit, is instead an access to telco network that uses T1 as physical layer, just like a data circuit does. So you would say correctly, a data T1 would support up to 20 calls of VoIP w/ G.711 codec. Then, you can put in play VAD that drastically reduces bandwidth allocation using the same codec. Remember however, that generally users don't like VAD.
And if you are a registered customer, the interactive calculator reference in the above document.
Hope this helps, please rate post if it does