The filing describes how last year’s settlement, which transferred ownership of the IP for Skype’s underpinning P2P infrastructure from Joltid to Skype itself, resulting in Joltid, the P2P company operated by Skype founders Niklas Zennström and Janus Friis, making “an investment of $80 million in us”.

Skype has also invested $6 million in Rdio, Inc a new social music service founded by Friis and Zennström, and $10 million in Atomico Ventures II, LLP, a VC fund operated in part by the pair.

Skype does not say how much of the $100 million proceeds of an IPO would go directly to shareholders. The company is also vague about how many shares its major shareholders own, and only listed the owners that hold more than five percent. Those include: Silver Lake Funds, eBay, Joltid and CPP Investment Board.

Skype intends to float to drive up user numbers and, along with them, paying VoIP customers. Skype has already recently been toying with making calls from mobile apps premium-only.

—It says the paid user base is up by 23 percent from last year - less than the 36 percent increase in the total user base.

—Paying customers were 8.1 million in June, of a 124 million average monthly user base - so there’s clearly room to grow…

—Total registered users is 560 million, so the majority of Skype accounts are no longer connecting - indeed, 20 million of them are people who automatically registered when creating a MySpace (NSDQ: NWS) account, and use Skype “infrequently”. “We have notified MySpace that we do not intend to renew our contract arrangement with MySpace, through which users can register through MySpace, when it expires on November 27, 2010,””

But, under a whole series of mandatory “risks” listed, Skype concedes…

—“Our connected users metric is subject to uncertainties and may overstate the number of users who actively use our products.”

—Also under “risks”: “Our paying user and communications services products billing minutes metrics are subject to a degree of inaccuracy due to fraudulent transactions and our method of calculating these metrics” ...

—“The peer-to-peer nature of our software architecture makes it difficult to determine certain operational metrics.”

—And Apple (NSDQ: AAPL) or its iPhone carriers “could withdraw (Skype 3G calling) functionality at any time or develop competing applications, such as Apple Face Time (NYSE: TWX), that may better integrate with Apple’s devices”.

Skype also admits that it’s subject to several intellectual property actions in multiple jurisdictions, including News Corp.‘s part-owned UK pay-TV firm BSkyB challenging the “Sky” in “Skype”.

Skype’s future success may also depend on remaining in the online telco sweet spot. In the filing it says: “If our business were deemed to be a regulated telecommunications business in one or more jurisdictions, it would significantly increase our expenses.”

But becoming a full-fledged telecommunications sector player is exactly what Skype wants to do to make its business go large.

The firm’s filing lists Google (NSDQ: GOOG), Microsoft (NSDQ: MSFT), Apple and Yahoo (NSDQ: YHOO) as competitors, and says of Google’s recent Global IP Solutions acquisition: “Google may use this technology to compete against us.”