Analysts for Piper Jaffray have been taking a look at what the agreement between Apple and AT&T could look like.

“While we do not know the exact details of the agreement, we conservatively estimate that AT&T gives Apple $3 per month (over the life of the 24 month contract) for every iPhone customer already with AT&T and $11 per month for every new subscriber,” lead analyst Gene Munster wrote in a note to clients.

Munster believes that these figures could add 2 cents to his per-share earnings estimates for Apple in 2007, 15 cents in 2008, and as much as 58 cents in 2009.

Munster also took a survey of 253 iPhones users, he found hat 52 percent switched from another carrier to AT&T.

“Our survey, however, consisted mostly of early adopters who would be more willing to cancel non-AT&T contracts than the general customer base,” he wrote. “For that reason, we estimate for the mix of iPhone users that are new to AT&T will drop from 52 percent in June to 44 percent in the September ’07 quarter and continue to drop over time as AT&T gains an iPhone user base.”

The analyst also predicts that Apple will sell 3.2 million iPhones in 2007, 12.4 million in 2008 and 45 million in 2009.

“These estimates may seem bold, but we believe Apple can garner 7.0 percent of the handset market share in North America and 2.8 percent share in the rest of the world by 2009,” he told clients. “We assume Street pricing on the iPhone will have dropped to $338 by 2009 from $542 in 2007. Additionally, it is critical to keep in mind that the iPhone combines iPod and mobile handset, which should attract more than just a mobile phone customer.”

The firm holds an Outperform rating on Apple shares with a price target of $160.