Not technically a hack, but Just a tutorial for those who want to integrate Google Voice transparently on their DROID and other Android powered phones.
1) First Get a Google Voice account here: https://services.google.com/fb/forms/googlevoiceinvite/
2) Log into it and click on the SETTINGS link in the top right
3) Click on the PHONES tab and click ADD PHONE
4) Type in the name fo rthe phone profile EG: MY VERIZON DROID or whatever
5) Enter the phone type, select MOBILE in the drop down box, and make sure RECEIVE SMS check box is ticked.
6) Click on SHOW ADVANCED SETTINGS and from there you can disable the need for a PIN code if you call to check Voicemail from your Cell Phone (If you want)
7) Finish by clicking SAVE you will be given a 2-digit number, click CONNECT and your cell phone will ring, an automated voice will ask you to type in the number given on the website, so type it in! if successful you should hear "Your forwarding phone is active" then you can hang up
8) You should still be on your Google voice settings page, on the PHONES tab. click the link right next to the new phone entry that says "ACTIVATE GOOGLE VOICEMAIL ON THIS PHONE"
9) a window will pop up asking you to "Switch your voicemail to google voice" the number of the cell should already be there, but you have to use the drop down box to select your carrier (Verizon for Droid users) and click continue
10) the window will change to an activation screen with a number *71########## (Where # is your Google voice number) so grab your phone, and enter that exactly as shown, and press CALL as if you were calling someone. It will connect and then it will hang up, an dyou're done with that.
11) Grab your phone and go to the Android Market and search GOOGLE VOICE and download the official GV app. Install it.
12) Install it, and set the phone to USE GV FOR ALL CALLS in the GV SETTINGS
13) Go back to your Google Voice page, click SETTINGS and click the VOICEMAIL AND SMS tab.
14) Disable Voicemail transcription if you want, or pick SEND AS SMS or FORWARD AS EMAIL. Whatever is your pleasure.
15) Now grab your cell phone again, and open up the default sms text program called MESSAGING and press the Menu key, then click SETTINGS and make sure DELETE OLD MESSAGES is checked, then scroll to the bottom and UNCHECK the NOTIFICATIONS box.
16) Now make a link to the Google Voice Application on the Home Screen or wherever you used to have your MESSAGING icon.
What this does is it sends SMS to both Google Voice SMS AND to your carriers SMS system, which forces the Google Voice application to check for new messages so they are delivered INSTANTLY instead of having it find messages at intervals which is slow, creates conversational delay, and wastes battery.
(sms tip is from robertbaker13 on google forums)
17) LAST STEP! make sure all of your numbers are in 10-digit format EG: 6195551234 if your numbers are in any other format EG: +16195551234 or 5551234 then your Google voice Number will not show up on their Caller ID INSTEAD your actual carrier # will show up and confuse people if you're trying to use GV as your primary contact number.