Social payments startup Venmo is introducing Siri voice commands, a feature that will give its iPhone 4S user base the ability to send payments to friends with just their voice — and, of course, the help of the iPhone’s beloved virtual assistant.

Venmo is a two year-old startup that aims to make splitting bills and paying friends via mobile easy and enjoyable. With the addition of Siri integration, developed by engineer Andrew Staub, the company now provides users with the most novel way to pay.

“Venmo was originally built as a way to pay your friends with text messages,” Staub told VentureBeat. “We developed our Siri integration on top of our text payment system. We are taking advantage of Siri’s ability to send text messages, which any developer can use. It took us about a week to alter our text parsing system so that we could interpret a message that took advantage of Siri’s optimizations for contact names and dollar amounts.”

Here’s how it works: Once you’ve saved Venmo as a contact in your phone, you can begin commanding Siri to do your payment bidding. Try saying something like, “Tell Venmo to send Jennifer Van Grove $5 for being an awesome reporter,” and you’re golden. Siri will then draft a message for you to review and send, and you’ll receive a confirmation message when all is said and done.

Of course, the say-to-pay functionality will only work if Siri is in a cooperative mood. Last week, the virtual assistant decided to temporarily shuck off her assistant responsibilities. Should that happen again, you’ll be stuck with paying the old-fashioned way. Whatever will you do?

[Image via Will Hastings]