if you want to develop some application for your iphone, you need Phone SDK

With this software you can develop applications that run on iPhone and iPod touch. Includes the Xcode IDE, Instruments, iPhone simulator, frameworks and samples, compilers, Shark analysis tool, and more.

NOTE:
· In order to download this application, you need to log in with your Apple ID.
· You must be enrolled in the iPhone Developer Standard or Enterprise Program to access the development resources for iPhone OS 3.0 beta.

WARNING: Before installing and developing with this version of the iPhone SDK, you must first upgrade your Mac system to Mac OS X v10.5.5 or later.

How about Iphone OS 3.0 yeah this way maybe little be piracy, so do it for purpose only ( Dont trust the last word ! :D )

I got from here

Download iPhone OS 3.0 GM 7A341 (Gold Master)

Usual Warning: Use at your own Risk

Download iPhone OS 3.0 GM Seed 7A341 Gold Master for iPhone 3G

ipsw file (RS links)

iPhone1,2_3.0_7A341_Restore.ipsw.part1.rar
iPhone1,2_3.0_7A341_Restore.ipsw.part2.rar
iPhone1,2_3.0_7A341_Restore.ipsw.part3.rar

Download iPhone OS 3.0 GM Seed 7A341 Gold Master for iPhone 2G

ipsw file (RS links)

iPhone1,1_3.0_7A341_Restore.ipsw.part1.rar
iPhone1,1_3.0_7A341_Restore.ipsw.part2.rar
iPhone1,1_3.0_7A341_Restore.ipsw.part3.rar

Download iPhone OS 3.0 GM Seed 7A341 Gold Master for iPod Touch 2G

ipsw file (RS links)

iPod2,1_3.0_7A341_Restore.ipsw.part1.rar
iPod2,1_3.0_7A341_Restore.ipsw.part2.rar
iPod2,1_3.0_7A341_Restore.ipsw.part3.rar

Download iPhone OS 3.0 GM Seed 7A341 Gold Master for iPod Touch

ipsw file (RS links)

iPod1,1_3.0_7A341_Restore.ipsw.part1.rar
iPod1,1_3.0_7A341_Restore.ipsw.part2.rar
iPod1,1_3.0_7A341_Restore.ipsw.part3.rar

Need some tutorial  now

#updated

If you want download all series firmware of IPOD from apple, you need check out for Download Ipod firmware, Must know for jailbreaking