WhatsApp, the hugely popular cross-platform messaging system available to Android and iOS, saw out 2012 with an incredible bang. The company has announced that it processed a staggering 18 billion messages on New Year’s Eve alone, exceeding its previous record of 10 billion messages processed last August.

WhatsApp saw 7 billion messages delivered inbound on December 31, plus 11 billion going outbound. Why the difference? Well, that’s all because of group messaging. WhatsApp explains, “sending one message into group chat of 10 people is 1:10 inbound:outbound.”

WhatsApp is one of the most popular messaging services for mobile devices, largely thanks to its support for so many platform. Users with an Android, BlackBerry, iOS, or Windows Phone handset can install the app and send and receive as many messages, pictures, and videos as they like completely free (providing they already have a data connection). Many see it as a cheap alternative to text messaging.

It’s hardly surprising the service became so popular on New Year’s Eve, then, a day when phone calls and text messages surge as everyone wishes their friends and loved ones a happy New Year.

In comparison, O2, one of the U.K.’s top four carriers, saw text messages increase by 27% across New Year’s Eve and New Year’s Day. The 440 million text messages that were sent across its network is 10% more than it saw the same time last year.

• SourceWhatsApp on Twitter