I'm having the same issue...I found this info that may be helpful.

http://www.irs.gov/taxtopics/tc556.html

I found one question from Becker:

Rona Corp. 1998 amt income was $200,000.  The exempt portion of Rona's 1998 income was (assume Rona does not meet the definition of a small corporation):

a. $0   b. $12,500   c. $27,500  d. $52,500

ANS: c

Explanation:

Initial exemption amt is $40,000

Exemption Limitation: AMT income $200,000 - $150,000 Phaseout level = $50,000 * 25% Phase out %age = $12,500

So, $40,000 - $12,500 = $27, 500.

Thanks nacol -