First of all, and most obviously, it’s essential that you read all the small print before your sign, so as to ensure that your business isn’t hit by unexpected charges and fees.
You should also consider the time implications of a contract before signing it. Long-term contracts that lock you in for more than one year can be a disadvantage, as they prevent you from jumping at a better deal if it comes along.
Before finalizing a deal you should make sure that you fully understand the cancellation policy, and how much it will cost to discontinue your service before the contract expires.
Finally, it’s important that you ask your provider of choice what their procedures are for after-hours technical support. If your phones stop working on the weekend or in the middle of the night, will someone be available to fix them? Don’t sign anything until this question has been answered to your full satisfaction.