Devices running Apple's iOS, the main competition for Google's Android OS, are expected to power the largest chunk of the search giant's mobile revenue and will represent two percent of the company's total revenue for 2012.

Senior Analyst Gene Munster at Piper Jaffray said in a note to investors on Wednesday that he estimates Google will take in some $4.5 billion in mobile revenue over the year, $500 million from display and $4 billion from search, and Apple's iOS platform is set to be one of the biggest contributors.

Munster calculates that if iOS accounts for 40 percent of Google's mobile profits, which equates to $1.6 billion, the net after TAC would be half that or two percent of the company's total revenue. The estimate is conservative compared to a March report that found 80 percent of Google's mobile revenue came from iOS while Android only accounted for 20 percent.

The analyst also notes that Apple's rumored switch away from the iOS Google Maps app to a proprietary mapping solution is unlikely to affect mobile revenues for either company. The change would further minimize Google's presence in iOS as its Maps app came pre-installed on all iPhones since the handset was first released in 2007.

Interestingly, Munster believes that Google Maps will still be available through the iTunes App Store, which is also home to other products like Google+, Gmail and Google Search. It remains unclear whether the app will be found to replicate features already offered by iOS which would give Apple cause to reject it under the App Store's guidelines.