Outgoing calls with your Google Voice Caller ID
One of the more interesting aspects of Google Voice is that you can make outgoing calls and the people you call will see your Google Voice Caller ID. There is a gotcha here, though.
In order for this to work, you must be using the Google Voice app. That means, for example, if you get an email with a phone number in it, you need to be diligent. Clicking that phone number will dial out using the iPhone's native dialer, and will reveal your iPhone phone number to the person you're calling.
Instead, you'll need to copy and paste (or remember) the number in your message, switch to Google Voice, enter that number in, and dial. It's a total pain, but it's a small price to pay to have control of your outgoing Caller ID number.
The good news is that the Google Voice app has good integration with your contact list, along with its own Quick Dial section, so for outbound dialing to your regular contacts, you're golden.
One other point about this. There's been some confusion, because when you dial out using the Google Voice app, Google dials some random phone number someplace in America. Then, through that and the magic of undisclosed Google data centers, Google Voice completes your call. That number is how Google Voice accesses the phone system, but it's not the number that shows on Caller ID. So there's at least something you don't have to sweat.
It should be noted that outgoing calls still use your minutes, so keep that in mind. There is a way to make outgoing VoIP calls via WiFi, which I'll discuss below, and that won't cost you any minutes.
I put the Google Voice app on my little iPhone tray, so it's easy to get to, and I remember to use it as a replacement for the iPhone's own Phone app.
Do not disturb
One interesting feature of Google Voice is its Do Not Disturb feature. You can enable this for the application, which means you can prevent calls from coming in, while you're still able to hear the sounds of pigs dying at the hands of bizzaro birds.
Making sure you get SMS notifications outside of the Google Voice app
If someone texts you, it's nice to get a notification. You can enable this in Google Voice, but it's buried pretty deep. In one install, I found that notifications turned on automatically, but in another, I found it didn't.
To enable notifications, go into the Google Voice app on your iPhone, tap Settings, scroll down to under "This phone" and tap "This phone's settings". On the next screen, slide "Text forwarding" to on.
No picture texting
There's one limitation here, and it's kind of unfortunate. Apparently, Google Voice doesn't support picture texting. For a free service, I have no problem with that. The disadvantage is that if someone texts you a picture, you get nothing. Not even a notification that anything was texted to you.
While I'd certainly like to see Google add picture texting, a good intermediate solution would be for Google to intercept the picture message and send a simple text message to you, saying you got a picture text, but Google Voice doesn't yet support MMS. Google, consider this an important feature request.
Calling other phones from your iPad and iPod touch
Like many Google products, there's are some arcane and unclear options available in the Google Voice app. One such option is the "Use Click2Call" button. I haven't used this, but from what I can gather, when you enable it, you're able to dial out from a non-phone device by routing your call through a nearby phone.
What happens is when Click2Call is enabled, and you're about to make a call, you're presented with a list of phones. The Google Voice app then makes a WiFi connection to the phone, and dials the call through that phone.
Convoluted, but it apparently works.
Minutes-free VoIP calls
Here's where things get interesting. If you have access to WiFi (and this is particularly interesting to iPad and iPod Touch users), you can make minutes-free voice-over-IP calls to phone numbers throughout the U.S.
You can also use this feature over 3G, but it might not be wise unless you, like me, have an unlimited data plan.
To make this happen, you're going to need another iPhone app, Talkatone, which is a free download. Beyond in-app ads, I'm not entirely sure how these guys make their money (or if they do), but this free app and free service will give you free Google Voice VoIP, right on your iPhone.
It's a worthwhile download.
Fun with other platforms
This post has been all about using Google Voice on the iPhone, but you can obviously use it on Android phones as well.
Google has also done a deal with Sprint where Sprint customers can use their existing Sprint phone numbers through Google Voice, with all the Google Voice features. I, personally, will never recommend Sprint after experiencing some breathtaking rudeness at the hands of their customer support people some years ago, but the company does field some impressive phones, which would work quite nicely with Google Voice.