Shall I attach any form other than 4868 to file extension to claim resident alien for tax purpose in 2008?
Thanks

IRS does not want to know why you are applying for extension. Do not attach any document with Form 4868 except payment check (if needed).

Thanks, MukatA!
If I claim Non-R alien, I need to write a check of over $2000 to IRS. So I choose to file extension and claim R alien after this June (then I can file jointly 1040 with my wife and get refund of over $3000).
So shall I mail extension form out along with a check of $2000? Or I'd better not to attach anything other than the form 4868?

I can not tell if you can file joint return as residents or not.
If you are sure you can do it, then calculate the tax based on the return you will file and report on Form 4868.

Thanks again, MukatA.
I don't understand what you meant: "if you can file joint return as residents or not".

I came to US on F-1 in 2005; graduated with master degree in Aug. 2007; OPT-- H-1B on Oct. 1, 2008; H-1B since then.
My wife came here on F-2 in 2006; went to school and transferred status from F-2 to F-1 in Aug. 2008; now she is on F-1.
So I figured it's much better to file extension and claim as resident, and then file joint return (1040) with my wife. Am I wrong?
I appreciate your help!

You have yourself explained what I meant by "if you can file joint return as residents or not;" now you have given more info about yourself.

Yes, you can file joint return as residents after you meet SPT in 2009. Read Your U.S. Tax Return: Substantial Presence Test (http://taxipay.blogspot.com/2008/04/substantial-presence-test.html)
You will also attach First Year Choice letter with your tax return.

Thanks