We wrote much of the material below in 2008 for a whitepaper, but things haven’t changed much. That’s why I want to give some advice to small companies that want to choose a hosted Unified Communications service; hopefully they will make a better choice.
The key is to always ask the service provider before taking any purchase decision. There is no perfect software or perfect  solution, but the vendor must be aware of that and he must know how to get closer to perfection. Enjoy the following questions and do not hesitate to ask them before choosing a hosted service. Although they look quite simple, you might be surprised about what kind of answers you will get.