Microsoft has released Send; An app which uses email for text messaging.
There are quite a few text messaging or IM apps available but none of them integrate with Outlook as tightly as Send. As Send uses email as the transfer method, all the IM messages that you send and receive will also be available in Outlook and you can use your existing Address Book to send message to people.
In essence, Send is a lightweight email app with an interface that is optimized for quickly sending those short back-and-forth messages.
Currently, Send is only available for iPhone in the US and Canada and you need to have an Office 365 for Business or University email account. An app for Windows Phone and Adroid is coming “soon” and the app will become more broadly available in the coming months (Read; To Outlook.com users once they have been migrated to Exchange Online).