Can I unjailbreak my iPhone 3GS WITHOUT messing up my unlock?

I want to unjailbreak my phone because it's slow and I don't care about cydia or changing and tweaking my iPhone. Its unlocked for straight talk. If I restore my phone will I lose my unlock? Will it mess my sim up? Can someone link instrutions on how to restore my iPhone?

All att iphones can use straight talk without it being unlocked.

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