We all use disparate messaging apps. Google, iMessage, WhatsApp, FB Messenger, Snapchat, TextSecure, Viber, even ancient Skype or MMS/SMS. A platform is only as useful as its number of users but I'd also like to add some requirements to what you use. It should have the option of encrypting all messages so AT&T or the NSA don't read about how much you loved your burrito at lunch. And it should be open source so the community can verify there are no back doors. It should also be cross platform and device; iOS, Android, OS X, Windows, Linux and web. Many have come close but only my extreme nerd friends use them.
I've had Telegram installed for a while but no one else uses it so I'm throwing it out there since a few respected tech journalist have started to share their use of it. It is OSS, it is free, you can encrypt, it covers all major platforms, has delivery receipts and it allows group messaging. I'm on it with my main Google phone number. Cheers.