First, though, I want to give a quick refresher on how Voice works. If you're not familiar with it, Google Voice is a web-based telephone system that does not replace your existing phones, but rather helps them work better. You get a new Voice number that (if you use it full-time) becomes your primary phone number. You then set your new Voice number to forward to your existing phones (home, cell, work, whatever) based on whatever conditions you set. For example, you can have it forward to your home phone on weekends, your work phone between 9 and 5, and your cellphone in the evenings. Or have it ring all of your phones at once. Or have it forward selectively based on who's calling. (Check out lots of videos on how Voice works at their YouTube channel.)
Anyway, using Voice full-time means that you have to tell everyone you know that you have a new number. That's the biggest downside, but it's not terrible. I switched about 3 weeks ago and have been using it as my primary number. Unfortunately, (or fortunately, depending on how you look at it), I don't have a landline, so I can't have Voice forward calls to more than one number (my cell), but that's okay. So what are the benefits of using it on a daily basis?
Number portability
This one is huge. My Voice number is mine forever and I can set it to forward to whatever other phones I want. This means that if we ever get a landline, or if we switch cellphone providers, I don't have to give everyone a new number. Ever again. This makes switching numbers, moving, etc. so much easier down the road.
Web interface
Just like Gmail, the Voice web interface provides everything you need to manage your phone calls and texts. You can initiate calls and send texts, reply to texts, view call history, view voicemails, change settings, etc. all from the website. And nothing is deleted unless you delete it, meaning that you can go back and view texts, voicemails, call logs, etc. from years ago if need be. Being from Google, it's all easily searchable, too.
Voicemail transcription
When someone leaves you a voicemail, Voice transcribes it to text automatically and very quickly so you can read it. To be honest, I haven't actually listened to a voicemail in a very long time. The transcriptions aren't perfect (and are often hilarious), but they're getting better with time, and they're usually good enough to get the idea of the message. Voice can even email the transcription to you every time you get a message. Transcriptions are also searchable from the Voice website.
Free text messages
All text messages sent or received through Google Voice are completely free, it's that simple. You can optionally have Voice forward texts to your cellphone (which of course does count as messages against your text message plan with your carrier), but you can also have texts forward to your email, or view them using the mobile app (which we'll look at next). So you can text as much as you want from the Voice website or the mobile app and you will never be charged. It's about time.
Mobile app
This is undoubtedly one of Voice's killer features. There are native apps for Android and BlackBerry, as well as a web-based app for the iPhone. Naturally the Android app is the most full featured, and might be one of the most compelling reasons to use an Android phone. The app alerts you when new voicemails/texts arrive, lets you view transcriptions, reply to texts, place calls, etc. The Android app even runs in the background letting you use the phone's native dialer, but still using Voice to place the call. The Android app was also recently updated to support push notifications. This means that if someone texts your Voice number, the app will alert you immediately, just as if they'd texted your old number.
Conditional forwarding
This is a feature that I have used very little thus far. Voice lets you specify detailed forwarding rules based on who's calling, the time of day, etc. So you can have calls from your mom forward to your cellphone, and calls from your boss go straight to voicemail, for example. :-) In addition, you can block unwanted callers (which is extremely cool).
Custom greetings
Voice also lets you create custom voicemail greetings for different callers. So you can have a casual, funny message that plays when your friends call, and a professional message when your coworkers call. As an aside, this is a great way to mess with people who don't know you have custom greetings: "Hey, Bob, I don't feel like answering your calls at the moment. Leave a message."
Even more
Voice has lots of features that I don't want to go over in detail. Things like call screening, listening in on voicemail messages, call recording, conference calls, voicemail sharing, etc. Most of these are features I haven't used yet, but they're there for anyone who wants to use them.
Downsides
There are very few downsides to using Voice full-time, but they are worth mentioning. First of all, you have to contact everyone you know to tell them you have a new number. Annoying and time-consuming, but not really a downside, per se.
Another downside is lack of MMS support. At the moment, Google Voice does not support picture messaging. They've said that feature is coming, but for someone who uses MMS heavily, Voice won't be a good option for now.
Lastly, there's the ever present possibility of downtime. By routing your calls through another service, you're adding a link to the chain. If Google Voice ever goes down, all of your calls and texts won't work. This actually happened for about 30 minutes several days ago, but luckily it was early in the morning, so few were affected. Obviously, downtime is possible for standard carriers, too, but adding Voice into the mix definitely increases the chances.
Conclusion
Switching to Voice full-time is definitely something I'm glad I did. The downsides are few and the advantages are worth it. And I'll really see the benefit when it comes time to switch cell carriers and I don't have to tell anyone about a new number.
Voice is still in beta, too. There are lots of exciting features on the horizon (like VOIP!!), so the advantages are only going to increase. If you come back and read this post a year from now, you may laugh at what Voice used to be. I'm looking forward to it and I think everyone should check it out!
(P.S....before you ask, no, I don't have any Voice invitations left) :-)