The next question come down to features. If you know Cisco, I would probably stay with Cisco. I have a CCNA and consider myself a switch/router guy. It was realativly easy for me to transition to voice using Cisco Call Manager.
What kind of router do you have? Do you have any extra ones?
You may already have everything you need to run Call Manager.
There is a slightly stripped down version call Call Manager Express that runs on Cisco routers. It works pretty well but doesn't carry all the features of Call Manager. Call Manager runson HP and IBM servers and it pretty cool. The PRI is a plus.
If you decide to use Cisco, look at the MC3810 as a possability for terminating your PRI. They are a little old, but darn cheap and work well. You can buy an extra one off of ebay for little money as a backup.
It is what it is!!
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A+, Net+, I-Net+, Certified Web Master, MCP, MCSA, MCSE, CCNA, CCDA, and few others (I got bored one day)