VoIP Voice codec bandwidth comparisation when Trunking calls:

G.711 (ISDN - PCM)

one call: 164333.75 bps/94.26 pps ( 82.1 kbps bandwidth)
two calls: 296171.60 bps/101.46 pps (148.0 kbps bandwidth)

For every additional call: 131837 bps (65.9 kbps bandwidth)
Est. IP/VoIP Trunk overhead (Only first call when trunking): 32495 bps (16.0 kbps bandwidth)
Raw number of calls per megabit: 14

G.726 (DECT - ADPCM)

one call: 102412.85 bps/97.28 pps ( 51.2 kbps bandwidth)
two calls: 170242.49 bps/102.46 pps (85.1 kbps bandwidth)

For every additional call: 67847 bps (33.9 kbps bandwidth)
Est. IP/VoIP Trunk overhead (Only first call when trunking): 34645 bps (17.3 kbps bandwidth)
Raw number of calls per megabit: 28

GSM

one call: 70958.16 bps/102.13 pps (35.4 kbps bandwidth)
two calls: 100455.23 bps/102.63 pps (50.2 kbps bandwidth)

For every additional call: 29497 bps (14.7 kbps bandwidth)
Est. IP/VoIP Trunk overhead (Only first call when trunking): 41461 bps (20.7 kbps bandwidth)
Raw number of calls per megabit: 67

G.729 (License fee apply)

one call: 60124.33 bps/101.26 pps (30.0 kbps bandwidth)
two calls: 79496.23 bps/102.85 pps (39.7 kbps bandwidth)

For every additional call: 19372 bps ( 9.6 kbps bandwidth)
Est. IP/VoIP Trunk overhead (Only first call when trunking): 40752 bps (20.3 kbps bandwidth)
Raw number of calls per megabit: 102

Note: When measuring bandwidth, "kilobit" is 1000 bits per second (not 1024) and a megabit is 1,000,000 bits per second