Network planning help for 3 servers located at my home

My home internet infrastructure: ISP ==> Cable modem ==> DDWRT router ==> my computers I would like to somehow use my connection to provide external access to three different servers located in my home. I will have the following servers: 1. Vicibox/Vicidial server (based on Asterisk) where users can use their softphones to register to. Will have its own static IP. 2. A separate Asterisk server where users can use their softphones to register to. Will have its own static IP. 3. An OpenSIPs/Asterisk server where users can use their softphones to register to OpenSIPs. Will have its own static IP. My issue is I am unsure whether I need 4 separate internet connections to make this work (one for personal, and one for each of the servers). Hopefully there is a way I can do some sort of setting magically on my router, so I would be able to get by with the minimal # of internet connections. My ISP provides me a sticky dynamic IP (same IP usually lasts for about a year). Perhaps using DYNDNS would be a good way to keep IPs static. Also, I heard that OpenSIPS has problems behind router. Was hoping someone with expertise can provide some consultation regarding what is the best setup for my situation. Also, I'm not even sure I need to have three separate servers. I know I need to have the Vicidial server separate. But for the other two: one is an autodialer that users can register their softphones to, and the other is an OpenSIPs server that a user registers their softphone to where every X minutes Asterisk will call that softphone automatically to measure call quality (kind of like a speed test server). I'm thinking that these servers might be able to combined as one.