iPhone Headed to Verizon in 2010…or 2012

So, the iPhone’s next big feature?

Verizon.

This according to Piper Jaffray analyst Gene Munster, who says there’s a 70 percent chance that the carrier will add Apple’s super-smartphone to its lineup by the middle of 2010.

With AT&T’s (T) exclusive deal to carry the iPhone in the U.S. expiring next year, Apple (AAPL) has certainly considered such a move. It would be silly not to. Verizon’s (VZ) postpaid subscriber base is not only larger than AT&T’s, it’s untapped.

That’s an important differentiating factor given that Apple has an diminishing opportunity to attract new iPhone users from AT&T’s subscriber base. Says Munster: “Currently, the iPhone is available to 82 million AT&T subs in the U.S.; adding Verizon would more than double the addressable market, adding 89 million U.S. consumers.”

That’s certainly a compelling argument for signing Verizon up as an iPhone carrier, though whether Apple will do so remains to be seen. As Munster himself concedes, there’s a 30 percent chance that the company won’t ink a deal with Verizon.

According to other observers, that’s a conservative estimate. Kaufman Bros. analyst Shaw Wu said recently that 2010 is an unrealistic ETA for a Verizon iPhone. 2012 is far more likely, according to Wu.

“While we believe VZ is likely inevitable at some point when 4G technology rolls out in 2012 or so, we believe Sprint and/or T-Mobile are more willing partners for Apple in helping maintain margins and customer controls,” the analyst wrote in a note to clients. “From a technology perspective, we believe T-Mobile may have an advantage with a similar 3G UMTS/WCDMA network as AT&T.”