Mobile messaging company mig33 has raised $13.5 million to push its mobile social networking platform into the U.S. After receiving a $10 million round of funding last year, the company moved its operations from Australia to Burlingame, Calif. Now, with an eye on what CEO and Co-founder Steve Goh calls the “different dynamics” of the mobile environment in North America, mig33 is developing a web-based platform that will augment its existing mobile platform.

The company has a beta site that features numerous web-enabled aspects of mig33’s services under development, but Goh declined to offer additional specifics. He was, however, quick to point out that the U.S. market may have one social network too many, so it doesn’t sound like mig33 plans to compete directly as a social network (mig33 already has a WAP site).

At 9 million, mig33’s users total less than a fifth of Facebook’s, but the company’s services are available primarily via mobile download, which imposes a higher barrier to joining than simply typing in an email at a web site. That makes the current user base for mobile IM, email and VoIP pretty impressive. Goh didn’t disclose how many of mig33’s users are in the U.S., but said the company has 2 million users in South Africa and a large following in Southeast Asia.

Goh anticipates that the coming year will be a pivotal one in the U.S. mobile market, with sleek new handsets influenced by the iPhone as well as a realization by handset makers that getting developers and cool applications on a phone needs to be easier. Moves such as Google’s launch of Android as well as yesterday’s announcement that Nokia is buying Trolltech, underscore for Goh the rapid changes that should bring more apps to mobile phones in the U.S.

As for the current challenges of developing for several mobile platforms, Goh shrugs it off. “I grew up writing in Fortran so it’s reminiscent of developing in the early days of computing,” he says. Today’s developers may not agree, but one can’t expect Goh to bite the hand that he hopes will feed him.