On Saturday September 25th, after months of hard work, our Windows Phone client went live in the Marketplace!

WhatsApp Messenger for Windows Phone is available to those running version 7.5 (Mango) release on their device. We are sorry if you don't have Windows Phone 7.5 yet, but very soon all of the current Windows Phone 7.0 devices will get upgraded to 7.5 and you will be able to download and enjoy our app.

Also, Windows Phone client release brings our total supported mobile platforms to SIX! Just to recap, they are:

• iPhone (OS 3.1 or newer)
• Android (OS 2.1 or newer)
• BlackBerry (OS 4.5 or newer)
• Nokia Symbian S60 (3rd Edition Feature Pack 1 or newer)
• Nokia S40 (6th edition or newer)
• Windows Phone (OS 7.5 or newer)

We are extremly excited to add Windows Phone to the list of supported platforms. Stay tuned for more features and improvements...

We usually don't use this blog to talk about the technology stack behind WhatsApp, but today we wanted to share with you an awesome milestone we have reached.

Over the past few months we have been making a lot of improvements to our servers to increase the performance, uptime and scalability. Today we have tuned some knobs, shifted some traffic around and achieved 1 million established tcp sessions on a single machine (and with memory and cpu to spare!)

$ netstat -an | grep -c EST 1016313

We are extremely proud of this achievement and wanted to share with other tech minded people out there. For those curious how we did it, the technology on the backend is simple: FreeBSD + Erlang

P.S. - we are hiring in both client and server teams, so send your resume to jobs at whatsapp dot com if you are interested.