Besides being contactable, you also need to take into consideration which type of communication medium; for instance email or telephone, that will let you achieve the greatest business efficiency.
Communication components such as a leased landline, fax, WiFi router or internet service are now almost compulsory within the premise of business offices. These hardware and network equipment are the "baseline" communication platforms to start a robust and scalable physical infrastructure for your company. You might also want to consider the Singtel i-PhoneNet solution, which delivers enterprise-class telephone features through the cloud.
You also want to make sure that you choose the right vendor to implement each of your communication medium. With the right vendor, you can reduce costs, while making sure that your business is well equipped with the latest technology for improved operational efficiency.