There are plenty of phone apps to help you locate bars to drink in, but not too many that let you actually buy the drinks. My Shout is an Australian-developed app that lets you select drinks, nominate friends from your contacts you plan to share them with, pay for them via PayPal, and then collect them at the bar by showing your phone to the bartender.
There's a few obvious uses for this: you could organise the first round of drinks before arriving; send drinks to friends if you can't make it to a celebratory event; order while seated and then collect drinks as each person wants their next round; or pre-order
My Shout is a free download for iOS only. Right now, it's limited to a handful of venues in Sydney, but the developers say they hope to expand to other cities in the future. If you give it a try, tell us about it in the comments.
MyShout [iTunes Store]