I'm confused about when to file a dual tax return.
Two similar situation:
-person A arrived in the US in Feb 2010 with a J1 visa from Italy with a post doctoral researcher position. This person can be considered as a individual exempt as a trainee for the first two years in the US, and also treaty tax agreement for the first two years. Are the two years to be considered calendar or 365+365 days? Feb 2012 is the transition between exempt individual to resident alien. Should person A file a dual status tax return with a 1040 and a 1040nr-ez (and 8843) as statement?
-person B arrived in the US in July 2010 with a J1 visa from Italy with a post doctoral researcher position. This person changed from a J1 to H1B visa in July 2012. Should person B file a dual status tax return with a 1040 and a 1040nr-ez (and 8843) as statement?
Thanks a lot!

Non-resident alien status goes by calendar years.
If you exempted days of presence for the Substantial presence test in 2 out of the last 6 calendar years, you cannot exempt any more days.
So if you came in 2010 and excluded days in 2010 and 2011, you do not exclude any days in 2012 and would be a residnet alien once you meet the SPT counting all the days of presence in 2012.
So in your examples both persons would be resident aliens.

For the tax treaty: if the tax treaty has an exception to the savings clause covering the article you are basing your exemption on, that article would be valid for the time stated in the article (usually 2 years for researchers). So if you came on February 10th, 2010, you can claim the treaty exemption up to February 9th, 2012.

Note that if either J-1 visaholder is MARRIED, the option to file jointly is also available.