namirfathi, welcome.
A "cracked" iPhone may not be necessary. There is speculation that AT&T, Orange and others may be offering "unlocked" iPhone 3Gs. Personally I am not holding my breath for AT&T (not immediately at launch at least).
With that in mind, if you have an unlocked iPhone 3G, yes, in theory it should work fine with Etisalat.
My experience is that Etisalat actually has a more robust (and up-to-date) 3.5G network than AT&T anyways. So one might argue that the iPhone will actually work *better* with Etisalat.
Time will tell of course, it may be in your best interests to wait and hear about others experiences before you buy one.