If you want the full Google Voice experience - free and web-based SMS/text messaging, transcribed voicemails, selective greetings and call filtering, and multi-phone mastery - and your cell service isn't with Sprint, you need to pick up a new phone number that Google supplies. And getting your friends, family, coworkers, and emergency contacts all switched over can be a serious pain.
But it's less obvious that you can also use Google Voice as a nice little side service; one that lets you keep your "real" phone number, but also has a few extra ways to contact people, keep nuisance calls at bay, and even make calls when your phone is dead or out of service range.
Give it out as your "Second-Tier Number"
If Google wants to give you a phone number in your area code for free, who are you to turn it down? Sign up for Google Voice, pick out a number, and start giving it out and updating it for companies and people you don't really want to have possession of your true cellphone number. Set up Voice to forward to your phone(s), but change one setting through the Voice web site to have it show your Google Voice number as caller ID. When you see your familiar Second-Tier Number show up, you know it's a call you can probably let it head to voicemail, as it's what you give out to stores, utilities, people you meet at conferences, and the like.
Keep it for oh-crud-phone-is-dead moments
You're at your parents' house with the terrible Verizon reception, or at a spot where your phone has just completely died. And now, of course, you need to text your boss (and/or significant other) and tell them that your phone is dead. Grab any handy device with Wi-Fi available, head to google.com/voice, and send them a text message from your Google Voice number, and sign it with your name or initials. They get the message, you get some breathing room to recharge or find that one corner of the kitchen where you get one bar of service. If you've got access to decent Wi-Fi, you can also make a call right from Gmail, entirely free.
Make cheaper international calls without Skype
Whether or not you even sign up to take a Google Voice number, you can use Google Voice to make seriously cheap international calls, without having to pick up a specialized calling card or work out a time when the other person can be on Skype.
Use your Voice number as a make-do conference call line
When people call your Google Voice number while you're on a call, you can pretty easily add them to the call and make it a conference. So if your workplace doesn't offer easy conference calling, let Google Voice handle the job for you.
Send group text messages without special software
There are quite a few apps that let you hold a conversation with groups of people on their phones - Beluga, Kik, GroupMe, and even Google+ (which just renamed its group messaging function from "Huddle" to "Messenger"). Some can work with straight SMS messaging, while others require everyone having the app installed.
But if you just need to quickly shoot out a message to a not-too-large group of people, use your Google Voice account. Sign into the webapp, click the "Text" button on the left side (or tap the "m" key on your keyboard), and you can type or paste in phone numbers, separated by commas, for quick group messaging.
Use it to trick annoying callers into getting blocked
Got a misinformed debt collector, overzealous charity, or other badgering callers that don't understand "Take me off your list"? Call them back from your Google Voice number, identify yourself, and they'll almost certainly take note of your new number and assume it's changed, as The Consumerist blog tells it. Then use Google Voice's advanced blocking powers to send those calls into a black hole, and help keep other Google Voice users from getting the same calls.
Kevin Purdy is a freelance writer, a former editor at Lifehacker.com, and the author of The Complete Android Guide.