Do you want to break carrier lock from your iPhone 3gs ? if yes, use Remote unlocking method to unlcok it . You can get it from any of the online vendors like
Superunlockcodes.com to unlock it . Installing i pad base band to an iPhone is risky process. After unlocking your iPhone 3gs, you can upgrade your iPhone ios . It won't gets locked to your carrier again . Because, the above mentioned method is permanent unlocking solution for iPhones .