setting speed limit on point-to-point t1?

hi all,

before implementing a voip solution, we'd like to simulate how well the data traffic over point-to-point t1 link would still be after a portion of bandwidth gets taken up by voip traffic.

i'm a contractor, and deal more with avaya voice gear than cisco data gear, so i need some insight into this. we were thinking that to simulate this, we could set a speed limit at the interface. please let me know if my thoughts are correct:

first thought was that unless the routers are back to back like a lab setup, we can't really mess with the timing since that's set in the service provider equipment. if they were back to back, then the "clock rate" command on the router providing the timing would do the trick (of course that's not the case).

so if the timing is done by the provider and we can't change that, we could set half or 3/4 of the timeslots to a group and doing so would pretty much be the same as simulating having half or 3/4 of our bandwidth carved out to the voip traffic.

does this sound about right to you guys?

thanks so much in advance!!