A Phrasal Verb a Day

"We're having a whip round for Bill's birthday. Would you like to chip in a few pounds for the collection?" "Sorry, can I just chip in. I couldn't help overhearing your conversation. I just wanted to say, you should buy an Oyster card and top it up every day. It's cheaper in the long-run" Luke's English Podcast - how to use the London Underground http://teacherluke.wordpress.com/2011/11/07/mind-the-gap-how-to-use-the-london-underground/