LINE Users Exceed 100 Million in 399 Days; Hosted Stamps Revenues Alone Exceed 350 Million Yen in a Single Month

So, where are brands putting their advertising dollars these days? TV? Newspapers? Facebook? - LINE is definitely a powerful contender for exposure and advertising yen!
At around 2:04 am on 18 January, 2013, the total number of registered users on LINE, the smartphone-based free voice calls and chatting app which is Japan's competitor to SKYPE and Viber, exceeded 100 million. The service was launched three months after the Great East Japan Earthquake and tsunami, in June 2011, so it took approximately 19 months, or 399 days for the service to grow to 100 million. Considering that it took Facebook 1,300 days and Twitter 1,100, LINE's growth is phenomenal. 
LINE Downloads
Approximately 40% of the users are Japanese, and the smartphone-based service is finding fans in Asia, the Middle East, and Latin America as well. The service can also be used on the PC and Mac, of course, but its core strength is on mobile devices. 
Another popular service in Japan is rival and gaming market leader, DeNA's comm. DeNA announced at the end of December 2012 that downloads of comm exceeded 5 million, a service released in October last year in 204 countries to compete with LINE. comm's edge is its claim to offer higher quality voice calls than LINE and that users can send messages via comm to friends who are not yet on comm, whereby the messages get delivered as email. 
LINE was kicked off in a bit of a haste to respond to a growing desire among Japanese people to "connect" after the disaster that devastated the Tohoku region. The popular "stamps" or cartoons and emoticons were not released at the time, but when they were, in October 2011, they significantly boosted the number of users. 
More Cartoon than Emoticons, Stamps has become a competitive advantage and key revenue earner for LINE

In response to there being many users using the bear and rabbit as a couple, LINE released a couple version of the two characters as an upgraded stamp series.

The stamps are not just emoticons, but use popular characters from animated films and mascots of brands. In November 2012, AppWoman reports that there are 3,200 such stamps on LINE at the time and revenues from the paid stamps @170 yen each, exceeded 350 million yen in September alone. That is more than 2 million stamps purchased in a single month. (Note: The Nikkei reports that the revenue is 350 million yen in two months...)
Excerpt from Nikkei Woman (see references section at end of article)
In addition to those, there are the "sponsored stamps" whereby brands offer their mascots and characters for use by their "friends" on LINE. They are a unique form of advertisement and LINE charges 10 million yen for such stamps to be posted for 4 weeks. This advertising medium is so popular, there is already a waiting list for businesses to secure slots. 
Yes, 100 million is a huge number, but what are their active users? LINE claims that 86.1% are active in a month and the daily active user rate is 50.0%. With users growing at a pace of 5 million every three weeks, there is no wonder that the stamp slots are full. 
In an interview with the Nikkei Business, NHN's CEO Akira Morikawa says that as users are not asked to declare their gender or age at time of registration, NHN does not know the exact age/gender breakdown and profiles of their users, but they feel that there are more women users while men are quite active as well, and with small businesses, some use LINE as the primary telephony platform among employees and as a mailing lists for announcements. 

In addition to free voice calls and chats, LINE offers game-playing, horoscopes, and coupons/vouchers through LINE Channel, a new service that was launched on 3 July 2012. 
LINE Game consists of role playing games (RPGs), puzzles, and games that enable users to collect and "grow" or "nurture" virtual pets, among others.
LINE Fortune Telling offers more than 200 different types of horoscopes, tarot readings, and romantic compatibility readings as well as a collaborated fortune telling service with popular women's magazine an-an.
LINE Coupon is a collaboration with Japan's leading coupon/vouchers provider for food and beverages, Hot Pepper Gourmet, operated by Recruit Co., Ltd. Users can search for restaurants and bars based on their locations pinpointed via GPS.
LINE Camera is akin to Instagram, and enables users to take photos with their smartphones, decorate and clip them, and then post them to LINE.
Usage for the various contents that require payments are transacted through the virtual currency, LINE Coins, which are purchased in advance. 
In July 2012, NHN announced that LINE is used in 230 countries and territories worldwide and that there are 1 billion messages posted per day. And that was before they added all the "Channels" as per above and became more of a SNS. 
If LINE is not yet in your media mix for Japan, then now is a good time to look into it, especially for the F1, F2, M1, and M2 groups of consumers. 
Nikkei: ユーザー1億人突破のLINE、今後の展開は? | nikkei BPnet 〈日経BPネット〉:日経BPオールジャンルまとめ読みサイト
Nikkei BP: 無料通話アプリ「LINE」のユーザー数が1億人突破、開始19カ月で大台に
AppWoman: LINEついにキタ!ユーザー1億人突破!