MobileBeat has a good summary of 4 current revenue streams from mobile apps

1. Paid subscription over time:….

2. Ad-supported: …

3. Traffic share or bundling: …

4. Virtual goods:

But there’s one missing: lead generation. Companies like OpenTable and Mint use mobile phone applications to provide leads for reservations or upsell to financial services.

Common to both these models is a web site that provides the main feature set of the service with the application providing additional location aware functionality and convenient access.

Lead generation, used in the right way will generate the most revenues for an application, next to virtual goods, because the value of the transaction can be significantly higher than virtual goods revenue, though transactions will be fewer and farther between.