Music identification app Shazam is turning into a real success story, with its executives saying it’s driving more than  quarter of a billion dollars in digital downloads across major online music retailers. Speaking at the Mobile World Congress in Barcelona, Shazam EVP Marketing David Jones said the service, which recently passed the 300 million user mark, tags about 10 million songs per day. Users are spending about $300 million a year on services such as iTunes and Amazon, with most of the revenue from purchased music. Jones said 20% of all iPhones in the U.S. used Shazam last month, with 30-40% in Europe. The service is currently adding about two million users per week. Shazam has run more than 200 ad campaigns for more than 140 brands, with campaigns running between $75,000 and $200,000. [HitsDailyDouble]