The platform had previously only been available through Sony's connected devices like the PS3, PS Vita and Bravia TVs, as well as on selected Android smartphones and tablets.
The iOS roll-out, first reported in March, is part of the Japanese giant's plan to spread its Sony Entertainment Network, which also includes movies, to as many devices as possible.
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Like Spotify, the service gives subscribers access to 15 million tracks, for £9.99 ($9.99) a month.
However, for a basic subscription fee of £3.99 ($3.99), there's a Music Sync option which scans your hard-drive for pre-owned music and playlists, making it an alternative to Apple's iTunes Match.
Crank-up the service
The launch of the app for iPhone and iPod touch - there's no iPad offering yet - will be a welcome boost for subscribers who access their music through the PlayStation 3 or other Sony connected devices.
"We want to let users pick up their favorite device and crank up the Music Unlimited service at any time," said Michael Aragon, VP and GM of Digital Video and Music Services at Sony.
"With the addition of the new iPhone and iPod touch app, users with a Basic or Premium subscription can listen to their favorite songs across a number of the most popular connected devices – in and out of the home."
Feel like giving Music Unlimited a try? You can sign-up for a free 30 day subscription on the website.