Google Voice (Free)
Besides making iPhone users jealous with a native app (instead of a Web-based version), Google Voice can be a life-changing service. It can unify all of your phone numbers and send you SMS messages via e-mail, while offering low-cost international calls.
On your Android phone, you can use Google Voice to get e-mail containing your transcribed voicemail, make calls from your unique Google number (which rings all of your phones), and embed voicemail messages to share. Even better, Google Voice integrates natively with your phone’s address book.