The following table provides a high level summary of how residential VoIP service compares to other alternative solutions for home phone service. The table compares this service to a regular landline, a bundled phone service from a cable company such as double or triple play, and a cell phone service. The cell phone is included as some people decide to just get rid of their wired phone and use their cell phone for all calls. Free services such as Skype are not included as they are not effective, like for like, landline replacements in our opinion.
Mobile clients are softphones optimized for a particular mobile OS and for being used in mobile situations. This means they're designed to switch easily between different cell and wireless connections on the fly. This means you can let your employees use whatever the cheapest wireless connection around them happens to be—and often that can be free. They also let your employees use your company's phone system on their own devices.
Some form of call center capability is often available, though many times either as a different product version or simply a higher pricing tier, so be careful before you assume you'll be getting those features. These capabilities are meant to support large sales or service desk staff and their need to route and process a relatively large number of incoming customer or user calls. That means complex menu trees, an auto-attendant for routing, and service queues. You'll probably find you need interactive voice response (IVR) capabilities, and that should be backed up by support for a live operator or some other type of human intervention.
A business phone system helps you to present a professional image to your customers. If you do not have a need for office phones or spend the money, you can still use a virtual phone system to project a professional look. This enables you to place a call directly to a mobile phone. It also has key features like voicemail transcription and automated attendants.