This should help - the URL of the ECB website which carries the URLs of all the UK local radio stations who are providing live coverage of the Twenty20 games.
Don't know how good they all are, but Ian Hall at Radio Derby is always good for a laugh ("In my day we wouldn't have stood for this twenty over nonsense. Cricket was all about the pies and cakes. What's spectators got to do with anything? Kids? Pah. Lock 'em up, blooming vandals.")
Don't think they'll work until just before the coverage is due to start (but I might be wrong). Enjoy.