We have been reviewing products recently and one area I would highlight is the differences in pricing when you get into the details.
Make sure you are clear on the number of callers, where they are coming from, if you wish to record (and where do you store the recordings), etc. Not every option is included......Caveat emptor as they say. Also; use the trials and run some tests.....
There are certainly a lot of options. The US Tech Soup has a great synopsis of 15 of the products. I believe it is a Webinar using ReadyTalk.
Dan.