Choosing a VOIP telephone system or provider can be a confusing and intimidating process. One of the first things you should do make sure you have some background knowledge of what VOIP calling is, and how it works. You should also have a good reason to change. The most common ones are price and quality.
Once you've decided to switch try to get recommendations from family friends or co-workers. A positive recommendation from a trusted source is invaluable. Look to see if there are any/numerous complaints about any companies you are considering with the Better Business Bureau. Another great website to visit is BroadbandReports.com. This forum has information from regular consumers and leading industry figures.
Before you sign a contract make sure you are aware of any and all fees and surcharges. Make sure you are aware of any specialized equipment you will need. Make sure you know what the service policies are and how to contact technical support and customer service. Lastly make sure you know the terms of your contract. Shorter contracts are usually better in an emerging technology field, but generally speaking they are also more expensive. Weigh the costs until you are comfortable with your decision.