What is an extension phone number? A phone extension is a short internal number assigned to an employee, a project team, or a department of your main business number. Features Prices Why Us Blog Features Prices Why MightyCallCan i add an extra extension to my phone number without hiring? Many people contact the phone company and pay a hefty fee for an extra extension, but it is possible to add an extra extension without hiring a professional. Phone problems are also a common concern, and many people pay monthly inside wire protection fees.How do i list an extension with my business number? Say your business number is the hilariously direct 123-4567, and you want your customers to be able to access your Sales department directly from certain campaigns or ads, you can list the extension with the number, posting 123-4567-12 as the number to call.Is a network extender right for you? If a network extender sounds like the right option for you, then contact your carrier (Verizon, AT&T, Sprint, T-Mobile, etc.) and they should be able to get you set up with the right extender solution.