Telegram is a new messenger built by Pavel and Nikolai Durov. They previously founded vk.com, Europe's second largest social network after Facebook (especially popular in Russia).

A Few Reasons Why It's Great

1. Unlike most other messaging apps their clients (Android, iOS) source code and the underlying protocols are released with an open source license (GPL v2)
2. The founders note that they have no intention of making money with Telegram If they ever run out of money they want to finance it with donations and non-essential goodies.
3. There is an API that allows anyone to hook into Telegram and build clients, bots and additional tools.
4. The open API has led to the creation of Mac, Windows and various other clients (eg. commandline) that allow you to use Telegram on multiple devices (with proper syncing).
5. Groups can hold up to 200 users (compared to WhatsApp that allows you to create 50 groups à 50 participants max.)
6. All communication in Telegram is encrypted and there is even an option to create “secret chats” that: won’t be stored on Telegram’s servers, can’t be fowarded and will delete themself after some time.

Currently available for iOS, Android, Mac & Windows there is really no reason not to make the switch.

Send me a message how you like it: +49176 64718250.
(It’s easy: just tap the number on your phone, save me as contact and I’ll appear in your Telegram contacts.)

Edit: Although it's not a completely decentralized service (as communication services should eventually be in the future) it seems to be a big step in the right direction.