I have a small security lab already. The infrastructure has a FRAMESWITCH (cloud) with three 2500 routers, one 1720 and two 2900 switches. I also have two uBR924, each with 2 FX0 ports and 4 Ethernet ports.
Do you also have a firewall to use? It may be beneficial for working with specific ports and some intricacies there. I would suggest setting up accounts with various permissions, so that you can also play with what is available for each.
You may also want to incorporate a couple "non-Cisco" phones to determine which are actually interoperable with the system. You didn't mention if your switches were powered or not, so be careful when you order your phones to determine if they are Power over Ethernet (PoE) or not -- or they won't work. Have fun and let me know how it works out!
Oh, yeah, one more thing. Check the code on all of your gear! A router simulator will help with other routing protocols that are not available on your uBR924's or 2500's, unless you have full code loads with all protocols on them.
This was first published in March 2006