GroupMe, which also made our 2011 list of New York City startups to watch, launched in October 2010 as a way to easily create an instant SMS style chatroom across all phones- smart and dumb. Last week, the startup darling added push-notifications, photos and location sharing to its popular group-texting app, available on both iPhone and Android.

Today, the 2.1 app updates include “Joinable Groups” which are open, publishable and visible to your friends within the app. Other GroupMe users can request to join and then be approved or denied by the group creator. They’ve also updated the app with a mutual friends feature, similar to Facebook’s much loved option. Overall, the new app is streamlined, customizable with nicknames and offers new user notifications (which can get a bit annoying).

Have you ever been in a crowd of 70,000 tripping fans? Co-Founders Steve Martocci and Jared Hecht’s have. In fact, their longtime love for the musical group Phish not only nurtured their friendship but sparked the need for a way to communicate with their friends at these shows. But the guys aren’t your typical treehugging ravers. Before launching GroupMe, Martocci and Hecht put their time in at GiltGroup and Tumblr, respectively, prior to each starting their own tech companies.

45439595 SXSW: GroupMe says its going global. First, it adds new social features.

Combining geeky brains with real person needs, Martocci hacked together the first version of GroupMe at a 24 hour hackday last year. It was an app so simple, your Grandmother could use it. And this ethos continues at GroupMe, even with the latest version of their app, which despite its new features — photo sharing, location sharing and Foursquare integrations, continues to work on dumbphones. But the biggest perk isn’t the photo sharing, location sharing or integrations (including the odd fact its even pulling in group name suggestions from FriendFeed), it’s the fact that their group chat app now also works over data plans.

This is huge because it means GroupMe is getting ready to go global. We have good word that the first stop will be Canada. “International support is coming soon, but the kind of coming soon that you can really count on,” says Martocci.

In January, GroupMe scored $10.6 million in Series B funding in a round led by Khosla Ventures. When asked what the hell a group texting app might do with all that money, Martocci underlines their mission to go global: “We have a huge global vision of bringing this product to market. We’re just going to keep delivering the product. Smartphone or no smartphone, we want them to experience it. We’re building our team, navigating the telecommunications world and scaling.” GroupMe is currently servicing over one million texts a day, and is likely using some of that 10 million to pay Twilio, the communications platform its app is built on.

photo 4 220x330 SXSW: GroupMe says its going global. First, it adds new social features. Looking forward, while personally not much of a broadcaster, Martocci wants to take advantage of the photo sharing space and says he’d love to add Instagram filters in a future build as well as Twitter, allowing users to tweet aspects of a GroupMe conversation.

There’s some amazing transitions that are happening in this space. A move from old networks to IP networks. I love what’s been happening with Android and what the iPhone set precedence for: the networks are opening up and people are available to innovate on them. People haven’t been able to do this combination of group, voice, photos, location etc. before. Knowing that one day your phone can be your wallet, your keys, and not just your communication platform, and probably all within just one year. It’s going to be hard to predict what can be. Trying to think too far out is crazy…

Steve Martocci

GroupMe has big plans for the upcoming SXSW festival. “We always get excited for live events,” says Martocci, “The Austin area is one of our biggest regions, as we were the official mobile partner of Austin City Limits.” For the upcoming SXSW, be sure to set up your group via GroupMe’s dedicated page to take advantage of lots of cool features like entry to private parties and realtime updates from the team. Add friends easily via your phone’s contact list, Twitter, Facebook or Email. Their new app is particularly handy in crowded areas; it detects whether you have a bad data connection and will prompt users to drop down to SMS.