I was on 4G smartone - 5GB plan for $210, any additional data if you run out is 100 per 1Gb, as my PCCW line at home is shite which means the wifi is shite so i usually use up all my data quite fast especially playing youtube Elmo songs to my kid so I upgraded to unlimited plan for just over $300.
I do agree with what BDW said but living in da jungles of clear water bay, for me only a few providers can get good signal here or i would have looked for a cheaper deal.I cannot understand people paying hundreds of $$ per month for 4G with data caps. 3G is perfectly fine and unlimited for $86 a month.