Instagram has reached 27m users and continues its mantra that the photo sharing app will come to Android “really soon”.

Instagram is a photo-sharing social network that is available only on the Apple iPhone. It allows people to take pictures, assign filters, and then post them to a variety of social networks, including Facebook and Twitter. In November 2011, the company had already amassed 13m members in its 13 months of existence. That number has now grown by 14m in five months.

Founder Kevin Systrom, who spoke about the achievement at interactive conference South By South West, did not disclose how many of those 27m users were active. He did, however, wave a phone in front of the audience that supposedly had the Instagram Android application on it.

The application has been long anticipated by Android users who have waited nearly 18 months for the software. But its estimated time of arrival remains the same as always: “Coming soon.” Systrom did note that the application was fast, however, and the company has “been able to put together one of the most incredible Android apps you will ever see”.

Despite the long turnaround time for Instagram’s Android app, the company may be looking into a Windows 7 phone version.

It is also rumored that the company is raising US$40m in a round of funding that could rocket its valuation from $25m up to $500m. It hasn’t yet figured out a business model, however — at least not one that it has mentioned publicly. According to a report in the Wall Street Journal, venture capitalists are reluctant to jump into the funding pool without first knowing more about Instagram’s financial potential. The company lacks advertising — a possible business model — and may be hard pressed to include ads in its photo stream. It could, however, monetise brands pages. — Meghan Kelly, VentureBeat