Take this from one of those "IT" guys that is the admin of the phone system.
Ensure that the place you purchase from is very experienced with the product you are looking at.
If you wish to have a look at my trials, peek in the Cisco forum and read about my adventure.
I did not push the VOIP system, I was happy with the functionality of our Toshiba systems, we just out grew them and needed more features for remote sites, which is how we ended up with the VOIP in the end.
If you are a single location, I would look at a regular system and stay away from VOIP. Though I am not familiar enough with the pbx systems out there to know which would tie into your Exchange server.
If you are going to look at VOIP, realize that you will most likely have to rewire the entire shop. Along with purchasing new network gear to support the phones. Which will get expensive fast, if your IT guy cannot do it themselves.
Coming from the IT guy, stick with what works and stay away from the latest and "greatest", there is a reason your system has run for 25 years....
