We have this friend, Cristina. She rocks. On nights out, we know to just hand her the check and she’ll take care of informing us how much we each owe. Usually we’re in a bit of a drunken stupor and doing math is about as appealing as, well, doing math. Thanks to Billr for iPhone, you can have your own portable Cristina at your fingertips (that sounded oddly sexual). No more splitting bills 50/50 when your buddy was ordering top-shelf drinks and you’re having a couple of Bud specials. Just enter in how much each person’s food and drinks cost (for up to parties of 16) and Billr handles the messy tax and tip details. Of course, you could also just go with a round of Credit Card Roulette and hope for the best.