Wayne; there are a few options that you have here. The simplest depends on a few things.
Currently with the 4 t-1s are they multiplexed as one connection to your ISP or are they muliple connections that are load balanced with your routing protocol?
If so, what's your routing protocol?
Are you running a dynamic protocol like EIGRP, OSPF or RIP that may be handling your load balancing across the 4 T-1s?
Oh; are they load balanced at all? What I'm getting at is do they ever max out?
If they don't and you're using the default queueing method (First in first out - FIFO) then it might be as simple as turning on weighted fair queueing. That gives lower bandwidth traffic a higher priority than high bandwidth. At 128K there is some risk that the Voice traffic could get downgraded which of course would be bad.
In that case you can do custom queueing; custom queueing uses "buckets" (queuing filters) and I think the simplest thing to try first would be to give your VoIP traffic #1 precedence and anything else would match #2. All you need to do is likely ID the ports that your VoIP is using and put that in the first queue list, if you wanted you could probably also use (or use instead) the IP address of your VoIP termination point in your office. Hosts destined for that box would have a higher priority than the rest.
Let me know if you need some help; I'm walking distance after all.
