It can be difficult for groups to keep in touch while on the go, but a new iPhone app offers a compelling solution. With Fast Society, people with mobile phones of any kind can coordinate using private group text messages, instant conference calls and easy location-sharing. Now available in the App Store, Fast Society is a free iPhone app that provides instant, private mobile group chat. Users simply pick a length of time for their connection — the duration of a concert event, say — invite some friends, and chat with them live via group text message. Anything sent to 32787 (FASTS) will go out to the entire group, but users can also send “CALL” and link up in an instant conference call. Location-sharing, meanwhile, takes just two taps. Group members who don’t have iPhones can use the app via m.fastsociety.com — it works with virtually any SMS-enabled phone and supports nearly every major US cell service provider. Fast Society currently works only in the United States, but it plans to expand internationally. One to partner with toward that end…?