Last.fm is a music streaming application available for most mobile and desktop platforms. Last.fm removed free mobile streaming several months ago and introduced a 30 day trial of the 'premium' features. Last.fm attached this 'premium' state to accounts so that only premium accounts could access the mobile applications' streaming functionality. However, only new Last.fm applications can tell whether or not an account is premium so only they can stop non-premium accounts from accessing streaming services.
The ability to stop non-premium accounts streaming was introduced with the 30 day trial in version 1.7.4 meaning 1.7.3 of the application can still stream music. It really is as simple as that. All you have to do to regain the streaming functionality is downgrade to version 1.7.3 which can be downloaded here.
There are a few drawbacks to using an earlier version of the application. Updates introduce new features and bug-fixes to applications meaning that early versions will not provide the best user experience. The release notes of Last.fm for Android can be found here so you can see what you'll be missing out on.