FORTUNE has summarized analyst estimates for revenue generated by iTunes in Q3.

Apple recently consolidated iTunes, Software and Services into one line item which generated $12.9 billion in fiscal 2012. That makes it the company's second fastest growing revenue stream and according to analysts it will surpass both the iPhone and iPad to take first place in year over year growth when Apple reports its Q3 earnings.

iTunes estimates were optional in our quarterly polling, but so far we've received numbers from 40 analysts -- 22 Wall Street professionals and 18 amateurs. Their estimates ranged from the high of $5.6 billion submitted by Jefferies' Peter Misek to a low of $3.3 billion from Sunil Shah, an independent from the Braeburn Group. The average estimate -- $4.17 billion -- is 30% higher than the $3.20 billion listed for the same quarter last year in Apple's "reclassified summary spreadsheet."

Notably, the Street is more bullish than amateurs for change. The professional analysts are predicting 33% growth while the amateurs are predicting 26%.

Apple is set to announce its fiscal Q3 2013 earnings on