What the best VoIP service has

  • E911 availability. Enhanced 911 service (E911) automatically provides the caller's number and physical address to emergency personnel. The best paid VoIP providers include E911 service standard, but some software-based VoIP services -- especially free ones, such as Google Hangouts (Google Voice) -- cannot be used to call 911.
  • Local number portability. Most VoIP providers allow customers to keep their original phone number, but this sometimes incurs a charge.
  • Alternate or virtual numbers. By choosing an area code separate from the one you live or work in, you may be able to save out-of-state friends and relatives some money, or establish a "local" presence for your business.
  • Calling features. Free features may include call waiting, call forwarding, conference calling, voice mail, caller ID, an online call log, do-not-disturb setting and more.
  • Compatibility with computer networks and software. Unlike traditional phone lines, Internet-based VoIP can integrate seamlessly with your computer, Microsoft Office programs, Dropbox and more. This can save time and hassle. For example, you might be able archive voicemails to the cloud, fax a document directly from Microsoft Word, etc.
  • Multiple lines. Some VoIP services only allow one line, while others have multi-line offers. For business users, some VoIP services impose a line limit (20 lines, for example), while others offer unlimited lines.
  • Fax compatibility. Not all services support adding a fax machine, and those that do may charge extra.
  • Prompt customer service. The best paid VoIP services deliver prompt help when something goes wrong. However, free VoIP services often slash this benefit -- you may find yourself waiting for sluggish tech support, or simply relying on user forums to figure out a solution to your problem.

Know before you go

What kinds of calls do you make? You'll need to assess what you're currently spending on local and long-distance calls (and Internet or mobile data service) to determine whether VoIP will save you money. Most VoIP services charge a flat rate for unlimited local and long-distance calls in the U.S., and many include Canada and Puerto Rico. Depending on the service, things can get more costly for international calls. Calls to international mobile phones may cost even more. If you need business-quality VoIP, you may need to upgrade your Internet service.

Will you keep your landline? Because E911 service isn't yet universally available, experts say you should consider keeping a basic landline or cell phone for emergencies. Be sure to include that cost in your usage estimates. In addition, a landline will usually still work during a power outage; VoIP will work only if it's hooked up to a battery backup.

Compatibility with other equipment and services isn't universal. For now, not all home security systems, TiVo boxes and satellite TV receivers with internal dial-up modems work with VoIP, so, again, you may not be able to retire your landline if you use it for these purposes.

Check for hidden costs. Most VoIP services include an adapter for your phone, but not all do, so be sure to check when comparing plans. Many services charge fees up front for setup and/or shipping equipment. Also, be sure to determine the costs you will pay for international cell phone calls, which are not included even in all-inclusive overseas calling plans. Also check the taxes and fees that will be added for your area.

Investigate trial periods and cancellation policies. Usually, you will be refunded your money if you cancel your trial within a specified minute usage and time frame. However, you may still be charged for calls not included in your plan, as well as for directory assistance, international cellular calls and possibly for deactivation fees and shipping charges to return equipment.