|VLAN's are really independant of the IP addressing.|
For example, I can (and I have) take an older managed Cisco 24 port switch, create 3 VLAN's and assign the 4 existing (the management VLAN, VLAN 1, is there by default) to ports.
For the sake of ease of use I do the following:
VLAN 1 = ports 1 - 6 = Bank 1
VLAN 2 = ports 7 - 12 = Bank 2
VLAN 3 = ports 13 - 18 = Bank 3
VLAN 4 = ports 19 - 24 = Bank 4
Now I have 4 banks of 6 ports each assigned to a different VLAN.
I now plug my work PC and my department laptop into two ports in Bank 1 (for example) and assign them the following:
I now open a command prompt window on both and ping each from the other. I add the -t switch to make that ping continuous. Both reply to the other's ping as expected.
I can now take those two, unplug them from Bank 1 and plug both into Bank 2. After a few lost replies, the pings start replying properly. I can do the same with Banks 3 and 4 as well. The same is true for changing the IP's. Leaving the units plugged into bank one, I can change their IP's to 10.0.0.1 and 10.0.0.2 (SM=255.255.255.0 still) and voila, pings will start replying again (well ok, I'd have to redo the pings with the new IP's, but they would indeed respond).
As long as the PC's plugged into the VLAN's have the same subnet, they can communicate.
If I move the PC to Bank 1 and the laptop to any other Bank, no communication.
It's worth noting I can do the above with our managed 3Com switches as well as our Nortel switches. The point being, the VLAN's are not tied to IP's, or MAC addresses for that matter.
after reading the previous replies - I had considered having them use the old switch for the PCS and the new switch for the phones - he would just have to run another 12 cables
That actually sounds like a better idea. Certainly it would be less hassle for you. Not only would you not have to learn about VLAN tagging, you'd also get to avoid learning how to use the managed switch. Which I'll tell you right now, can be a real hair puller depending on the manufacturer.
Where I work, we have separate outlets for VoIP and data. Which means a minimum of two RJ-45's per wall outlet. We've even color coded ours. Black is data, blue is VoIP.