Twilio, a Web service API for business phone applications, has raised $3.69 million in Series A venture capital, according to a regulatory filing. Union Square Ventures contributed to the round. Albert Wegner of Union Square Ventures and angel investor Dave McClure are now listed as board members.

Previously, Twilio had raised $600,000 in seed funding from the Founders Fund and a group of angel investors.

The service, which is free to try, seeks to deliver new ways for businesses to interact with callers, be they employees, clients, or partners. Simple phone actions like playing back audio for a caller, recording caller audio, and forwarding callers to alternate lines can be integrated into your company's telephone system. Beyond the expected, Twilio enables its clients to construct more complex projects that are only limited by the skill and determination of the person programming the system.

Nevertheless, Twilio's API is designed such that users with any level of Web development skills and any already-established infrastructure can take full advantage of it.

Already, this San Francisco startup boasts some big-name clients: Cheetos, Sony Music, Tumblr, and even one of the two major political parties here in the US, which uses the service for gathering support from citizens.

This latest round of funds will be used by Twilio for the expansion of its sales and marketing, while further developing its product.