What will a 3g mobile give me that a non 3g cannot?

On the rare occasions that i have been deprived of internet access, my old non 3g phones have been able to access the internet, do email, albeit a bit long winded. what are the advantages/disadvantages of 3g?
Answer
3g - 3rd generation is like looking at broadband in comparison to 2.5g which is like a dial up connection. the 3g network is not complete yet but is you set your phone up on an automatic network selection it should pick up the best it can get. apart from better speeds when surfing, you can also make and receive video calls and watch tv. if your going for a new phone a the mo, the newest technology is hsdpa - high speed data packet access. this is even quicker that 3g so it may be the way to go. i know its already available on the vodafone network