Another region phone number
If your company is located in one city, and cooperates mostly with clients from another one, connecting a direct number in this region will be the best solution.
For example, your office is located in St. Petersburg, and most of your contractors are in Moscow. We will connect you to a direct Moscow number with code (495) or (499). As well as for any other city of Russia and the CIS.
Your contractors won't need to call long distance and spend money on communication - whilst you will have more new satisfied clients.