Amazon.com is making its Flexible Payments Service broadly available today. The service, which had been in limited beta, lets third-party developers tap into Amazon's existing payment infrastructure -- letting them charge customers using the payment information and shipping address they have on file at Amazon.

It's an interesting addition to Amazon's cloud-computing offerings -- and opens up a new front in Amazon's competition with eBay, which owns PayPal (Amazon recently dropped the Bill Me Later payment option, after it was acquired by eBay. Bill Me Later lets shoppers purchase items online and receive a bill in the mail).

Amazon charges fees for use of Flexible Payments Service. As part of today's rollout, however, Amazon is offering developers who sign up for Flexible Payments by March 15 -- and launch their application by June 1 -- free payment processing for the first 90 days, until their transaction volume reaches $500,000.

Amazon is also offering a simplified set of APIs called Quick Starts to get developers started.

Interestingly, I just spoke to Vikas Gupta, the founder of a Seattle startup called Jambool, who is a former Amazon engineer and was instrumental in building the Flexible Payments Service. Jambool, which recently launched a payments platform for buying and selling virtual goods on social networks like Facebook, is itself a large user of Amazon Flexible Payments Service.

"I think Amazon is one of the more interesting players in the online payment space," Gupta said.