If you are a small non-profit looking for the most feature-rich, inexpensive way to give work phone numbers to your staff, Google Voice is the way to go. Pretty much everyone these days has a smart phone, and your staff can install Google Hangouts on their phones, which lets them make and receive calls as well as send and receive texts to and from US numbers for free. The voicemail is particularly useful, as the service sends speech-to-text transcriptions of voicemail to your inbox. I hardly ever listen to the actual message anymore since—while the transcription isn’t perfect—it is good enough to convey the gist of the message.
I travel internationally both for work and vacation. It’s pretty great to have a phone number that I can still use while traveling, since the service works over WiFi rather than the cellular network.
We just hired a contractor for our org who will be spending most of his time overseas. But with his new Google Voice number, we can call him or he can call us for free.
You do have to have another valid US phone number to use when verifying your new Google Voice number, but employees can use their own personal mobile numbers for that.