You just cannot put a ration on number of phone calls your employees will make in the office. Phone calls are infact a necessary evil in offices. They account to huge bills.

But some companies are providing VOIP facility along with business internet service. This system works on a large scale, so is best to be used for especially in medium and large business.

With business high speed internet if you also get VOIP facility that saves lot of money. VOIP will provide real phone company back up, and this is highly recommended for office and business purpose. 

Always choose a company that can offer you a complete package under one roof. T1 line is one of the necessary elements that the company should have. Above this if they even provide for T2 and T3 lines then it is even better. Because no matter T1 lines are a little expensive these days, but with its ever increasing utility, its popularity is also on a rise. It is quite possible that in coming future due to great demand of t1 lines, market prices will be shared and will fall down for consumers. So you should be the first on to upgrade from normal DSL lines to T1 lines to further T2 and T3 lines.

Infact it is always advisable to go for a service provider that is solely into this business. If their services are diversified, chances are they might not provide quality broadband wireless connections.