I am not sure, You need to contact the customer support of your network as why the internet did not work in your old flip phone.Maybe it had a lower frequency (2G) and you were on a 3G....I do not know the exact reason.But if you use your sim in iPhone 3G you will not face any problems,since its unlocked and a higher version mobile model.Recently,I unlocked my iPhone 3G using the support of Onlinegsmunlock.com and till now using my contract sim without any problem.