Location-based technology is an increasingly important feature for mobile applications, and the market continues to heat up — with the iPhone’s just-announced GPS technology, we’re already seeing the beginning of the new wave of location-based applications. Now T-Mobile Venture Fund (the mobile carrier’s investment branch) has made a $6 million investment in a location-based platform called deCarta.

San Jose, Calif.-based deCarta doesn’t make applications on its own, but instead provides the technology that powers other applications, including local search, mapping and location-based social networking. It’s competing with some pretty big players, including Yahoo’s FireEagle platform, which launched earlier this year. But deCarta, which was founded in 1996, says it has already staked out a strong position in the market — its technology supports applications that account for 90 percent of the location-based revenue at its carriers, including AT&T, Sprint, Verizon and a dozen more.

The company touts the range offered by its platform, which can power everything from off-board, server-based applications to “connected navigation” enabled by real-time, two-way connectivity between your smartphone and different data sources. I’m planning to interview chief executive J. Kim Fennell later today, and will update this post with more details on what makes deCarta’s platform stand out.

The company is going after substantial capital, too — it took in $15 million last year, and now it’s raising a second part of its third round. The T-Mobile investment appears to be a part of the larger round, which is targeted for $21 million, and the company says it will be announcing more investors soon.

Update: I just spoke to Fennell, who makes a pretty convincing case that deCarta is the dominant platform in this market. For one thing, there’s the customer list — not only are well-known location-based mobile applications like Loopt and Pelago built on deCarta, but the platform also supported Google Maps during its first three years.

Essentially, deCarta translates the geospatial data provided by companies like Navteq into a format that can be quickly searched by applications like Zillow (another deCarta customer). The other companies in this area died out because they started too early, Fennell says, which is also an issue that deCarta struggled with. He says that Yahoo’s FireEagle isn’t really a competitor, since it’s more socially-focused. (As we’ve written, FireEagle’s big selling point is allowing users to control what personal location data they provide to applications. On the other hand, the products are similar in that they’re both platforms for application developers.)

The real action is going to come from Nokia, Google and Apple, who have all been sending signals that they’re going to launch location-based platforms of their own — Nokia, for example, has agreed to buy Navteq. That’s pushing more carriers to support deCarta, Fennell says, because the solutions offered by Nokia and Apple will probably be tied to a specific device.

As for the funding, Fennell confirms that T-Mobile’s investment is part of the second tranche of deCarta’s third round. He won’t confirm the $21 million target, but he says the tranche will be “in that range.”

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