The location from where you intend to use your iPhone is another iPhone 3GS Unlock faq query. For instance, if your iPhone is from Europe, you may wonder if it is a must for you to be located in that area for you to be able to have it opened.
Most of the companies which help in opening iPhone do not place this as a requirement. They are able to have it unlocked from wherever you may be. What they do is that they will email you and after connecting it to iTunes it makes it possible for you to unlock it. For that reason your location at the time of unlocking becomes irrelevant.