There are two basic kinds of softphone: a "fat" phone that's coded to run only on a full-fledged PC be that a Windows, Mac, or Linux machine. This software needs a real desktop or laptop CPU and all the other accouterments associated with a full-on PC in order to perform its functions. The other kind of softphone is one designed for a mobile device. Mobile VoIP clients are "slimmer" than a desktop softphone, which really just means they're designed to look a little different and probably have a few less features since mobile devices aren't as powerful as desktop machines. But if you're looking to run your home phone off your mobile phone wherever you are, then a mobile softphone is definitely the ticket; so be sure to investigate whether you residential VoIP provider offers a dedicated mobile client, whether that client will run on your mobile device, and how much it'll add to your monthly service charge.
Similar to its popular small business VoIP solution, Ooma Office, the company touts its on-premises VoIP appliance to power its residential service. You'll find three versions of this device to choose from: the Ooma Telo, Ooma Telo Air or Ooma Telo 4G, but they all sit between your Internet router and your phones, making installation of this low-cost service plug-and-play.
VoIP service simply enables your phone calls to be transmitted and received over your home Internet connection instead of your telephone landline. This is perhaps why some people refer to the service as being an Internet phone service or broadband phone service. This does mean though that you need a high speed Internet service to be able to use VoIP for your phone service.