I came to the US in 2000 on a H-4, as a dependent of my father. When I turned 21 in 2006 I switched to a F-1 visa, and after graduation I worked from Jan 2007 to Dec 2007 on OPT. Would I file as resident or non-resident for 2007? Also my employer withheld FICA. I am from Pakistan. Would I also be able to claim $5000 deductible under the tax treaty? Thank you.

You will file as a non-resident alien, and WILL be able to claim the treaty exemption instead of the standard deduction.

Because you were under the F-1 visa, you were NOT liable for FICA taxes. Ask your employer to refund these taxes (it is NOT too late for him to do this). If he refuses, get the refusal in writing and then file Form 843 to get a refund from the IRS.

I can help you with this process professionally. Contact me by email if you are interested.

I am not sure that Majidnh can file as a nonresident as he is residing in the U.S. since 2000 and parents have been claiming him as resident.
Also as per Pakistan and U.S. tax treaty, there is no deductible. If he somehow files as nonresident, he will only get personal exemption.
He must pay FICA taxes and file resident tax return.

Disagree.

There have been multiple cases where foreign nationals have worked extended periods on work visa (L-1/H-1/H-1B), then came to the U.S. on a J-1 or F-1 visa. The previous time under the work visas has no effect on their current J-1/F-1 visa.

Since he is under a F-1 visa, he is exempt from FICA taxes.

There IS a $5,000 treaty exemption under Article XIII(1). See pages 24 and 44 of IRS Pub 901.

Yes, a person from Pakistan on F1 visa has an exemption of $5,000.

Noted!

Agreed!