Minimal, yet powerful

If there is a flaw, it is only that the app hides too much of its power. It doesn’t show a dial pad window, for example, because you simply use the number keys on your keyboard—including * and #—even during a call. There is no contacts list or buddy list, either; your contacts live in your Contacts app.
The app is simple and reliable. It supports the codecs and DTMF options required for various VoIP services. I have tested it with Vonage Business, RingCentral, and 8x8, with good results. Compared with other VoIP softphone apps, this is easily the most Mac-like. It uses built-in MacOS notifications for incoming calls; double-click the notification and click “Answer” to answer an incoming call quickly. It also provides a service which, if enabled in System Preferences, allows you to highlight any phone number to call it.
As with other VoIP apps, audio device selection can be a little tricky. It prefers to use the device you select in its preferences and does not follow your system’s default mic and speakers. This can cause a little confusion if you are trying to change devices in the middle of a call. If I were to ask for one feature, it would be a menu for quickly switching between devices, to help minimize fumbling.
I suggest going through the menus, learning the keyboard shortcuts, and checking the FAQ on the developer’s web site. There is some good information there, including how to tweak things like “Touch Tone” (DTMF) duration and interval, if required for your system.

thornrag about Telephone, v1.2.4