It works fine on 64k connections, okay on many 9600bps connections. T1 is way more than is necessary.
The correct answer here is that "it depends". Most multimegabit connections are underutilized enough not to introduce significant jitter to change VoIP behaviour, however specially when going to corporate networks where peak hour usage is very near or at available bandwidth the mechanics are different. However, in our experience VoIP performance is more often hurt by either broken router code or misconfigured devices in the path (route cache purges, duplex mismatches, etc.) than actual lack of bandwidth. If it does not cost you, it´s a good idea to let the VoIP packets first to a low-bandwidth link but putting serious engineering or money for hardware is not neccessary. Fancy queueing will give you more consistent performance when something else uses up the link(s). Pete