Answers (5)
Yes, you can definitely download applications apart from iTunes for your iPhone 3GS. There are several third party application stores from where you can download your favorite app not only for iPhone but you can also download the apps for diverse mobile platforms including Android, iPad, Windows and Blackberry. You can visit OpenAppMkt, GetJar, Handmark, Opera Mobile App Store and many others. You can take the reference from this site in order to get the long list of third party app stores. Hope this will help you.
But im not really sure if it works on iphone i hopes it does :D