I have an unlocked and jailbroken iPhone 4 with 4.0.2 on baseband 1.59 of course. My questions is, can i restore to a custom firmware 4.0.2 and keep my baseband so i can unlock again or will my baseband go to the next one?

Also, what is i just do the erase all contents and settings? Would that take the phone back to how it was when i bought and would just have to jailbreak and unlock it???

I spoke to an apple representative today and she told me that it would go back to they way i bought it, but i didnt tell her the phone is jailbroken, so thats why im asking you guys, What do you guys think? Dtube and Olethros i would really like both of your inputs here.

I considering this because my settings is crashing everytime i try to go into them.

Erase all content and settings usually makes things worse -- this removes iOS from the device entirely, so the only way you could go back to 4.0.2 is if you have an SHSH on file with Cydia for that iOS revision. Past that, you can't restore a 'custom' 4.0.2, but you can restore to 4.0.2 and block the baseband upgrade by using TinyUmbrella / TinyTSS and ensuring the TSS server is running beforehand. This will stop the baseband from being upgraded. You will still need the SHSH to restore 4.0.2 in this case as well.

The Apple rep was incorrect, doing an erase all content and settings leaves the phone in a non-booting, non-working state. It must be connected to iTunes and iOS must be restored to the device before it will resume normal functions. This is generally NOT a good idea for jailbreakers or unlockers as without an SHSH, your only option then will be to upgrade to the current iOS revision (4.2.1).

Thanx bro, i'll just use it as it is till something else comes out

No prob, but as mentioned, if you've got your SHSH you should be protected from just about everything except for the baseband upgrade. That aside, if you don't mind detailing some of the problems you're having with the device we may be able to troubleshoot the actual symptoms you're experiencing as well?