Apple is allegedly in talks with music labels to offer an unlimited music plan that would allow users to download as much music as they want for $20 per month:
The plan sounds similar to Universal's Total Music plan in which the cost of music is embedded into the music player itself. Based on the wording of this article, it seems Apple's version of the plan adds the cost on top of the iPod or iPhone.
The negotiations are currently being held up due to disagreements in pricing. Apple is reportedly only offering $20 per device, while Nokia is playing almost $80/handset for a similar plan. Other possibilities appear to include a subscription based service for iPhone users ($7-8/month, for example) with the capability to keep up to 40-50 tracks/year even after the subscription lapses.