When Apple (NSDQ: AAPL) announced plans to open up the iPhone platform to developers and make its many features available for third-party applications, location-based apps startup Loopt found an opening. With the new iPhone SDK, the social mapping and networking service saw an opportunity to harness the cell-tower triangulation features of the first iPhone and the GPS feature on the new iPhone 3G, all while reaching an audience that is very much in line with Loopt’s typical user. In a brief interview on Monday, Loopt’s co-founder and CEO Sam Altman talked about new areas of growth for the company, hiccups along the way and yep, you guessed it, impressive iPhone usage from Loopt users. “There are definitely new avenues and that’s why we like our position,” he said. The confluence of newer platforms in mobile and an opening up of the old have all benefited Loopt’s opportunity. “Location is the defining element in mobile… In the past six or nine months, location services have really caught the public… It’s gone beyond the early adopter phase”

iPhone adoption and usage: Adoption tapered off briefly because of an “invite sort-of-fiasco” where multiple contacts in iPhone users’ address books were being invited to use the service somewhat unknowingly. The feature, which gave the company problems almost immediately after the iPhone 3G was released, has been completely shut down for the time being. The company’s working on a better solution that will ask users if they really, really want their contacts to be Loopt in, if you will. iPhone adoption is on the ups again, but its overall popularity on Apple’s App Store ebbs and flows. As of today, Loopt didn’t even appear in the top 100 free iPhone applications list on iTunes, but that list tends to skew more heavily towards new applications since it only reflects the previous three- or four-day cycle, Altman explained. The iPhone’s “not where most of our users are coming from,” Altman said, but those that are using the device are sending many more bits through Loopt on average. “It just means that people with an iPhone must never put their phone in their pocket, it’s really crazy.”

Show me the money: “We’re doing location-targeted ads, which are really cool because if they’re done right, everybody wins.” Advertisers pay an average of 10 times more for ads that have a location-relevant component too, he said.

Typical user and most popular features: Loopt tends to target people in their 20s living in big cities. Altman pointed to four features that are among the service’s most popular: seeing where friends are on a map, text alerts that notify users when a friend is nearby, local content and the ability to link to other communities such as Facebook, AIM and Twitter. “The usage numbers on local content are really surprising for us and how much people are accessing that.”

• Mobile Social Network Loopt Sues Loop’d Network, Over Name Similarity
• CBS And Loopt To Launch Location Based Advertising Service
• Mobile Social Networking/Location Service Loopt Gets $8 Million Funding
• Sprint To Launch Social Location Service; Launches Interoperable Social Networking Service