IFAICT useage for voip in use seems to be anywhere between 106 kb/sec to 40
kb/sec but can peak up to 150 kb/sec. Depending on quality.
Syke apparently peaks at 100 kb/sec but is generally between 32-64kb/sec.
Tests I've done here with voip optimised for voice quality using:
http://www.testyourvoip.com/
show a useage of about 68 kb/sec. Which equates (I think!) to about 1
gigabit per four hours.
What are users real world figures?
Useage for voip and skype in practice 
Linear Mode
