While other mobile advertising networks have continued to be acquired, but InMobi has made a big bet on independence, raising a $200 million third round from Japanese conglomerate SoftBank.

The Bangalore, India company was founded in 2007, and built itself up selling CPM banner ads across devices. It has more recently expanded to payments, and to HTML5 ads via its acquisition of Sprout. Today, it is the self-proclaimed largest independent mobile ad network in the world, with strong traction on smartphones across the world. One recent report named it the largest mobile ad network in key European markets, for example, although it has only moved into North America in the last couple years. Founder and chief executive Naveen Tewari said today that his company is reaching 340 million consumers in over 165 countries through more than 44 billion mobile ad impressions every month.

Meanwhile, competitors have been getting snatched up — Admob to Google for $750 million and Quattro to Apple for $275 million in 2010, and Greystripe to Valueclick for $70 million in April. Other rivals have also been raising significant new rounds this year, though. Millennial Media raised $27.5 million at the start of the year, and Jumptap brought in $25 million in May,

InMobi is calling this new round the largest mobile investment of the year, which might be true if game developer Storm8 hasn’t yet closed the $300 million round it has been working on. InMobi has previously raised two venture rounds worth a total of $15 million from Kleiner Perkins and Sherpalo Ventures.

The money will go towards expansion in Asia, especially China and South Korea; it has already been busy hiring, as our readers will have noticed. InMobi is also one of the companies that has stood to benefit from Apple’s crackdown on incentivized app installs this past spring, although the company hasn’t disclosed revenue numbers.