im on a 3GB maxis data package.. with youtube, i easily hit 3GB and usually by the end of the week (6-7 days before reset cycle), i already consumed 80-90% in 3G watchdog T_T. It is sufficient alright but dont do youtube or DOWNLOAD ROMS and TETHER to laptop too much lol like what i did 

A simple example of mine based on normal use.. browse2 Android section here + garage sales for 1hour is already about 15MB, guessing got lots of images to load for sure.. My pattern of data on phone when out of home is twitter (tweetdeck), friendcaster/fb official app, Pulse reader for reading new stuffs, XDA app and few market apps..remember not to set auto check update in android market otherwise it will auto update apps even when on 3G. 3GB is sufficient for heavy phone user to read, absorb knowledge and socializing but dont do much on media. If wan to download, use tubemate to download and not to stream.

p/s : Anyone uses livejasmin app here? haha xD

just be careful of your first month bill as normally prorated..after the 7th of evry month, then u good to go..and most of the place now have wifi..now i'm using iValue 100 on my sgs2..just start activate the plan yesterday...so from today till 6th july, my data will be prorated..

sgs2 is a great phone..like others say, i also hate to need to sync mp3 or files..that's why my iPod shuffle just put aside got lazy want to sync with iTunes..i better get the china iPod where it can act as mass storage..i love the 11GB space in sgs2..i fill up with all my office stuff and the display of office document and pdf are superb...far beyond my expectation...

viber is not yet in the market.. its only for beta testing if u signed up (still can sign up for it) for the beta testing.. Whatsapp is free for 1Year on android and yes, its on the Market 

Firstly, ask yourself what you'd expect the phone to do?
Are you the geeky type who loves to experiment wt gadgets i.e. constantly customize the themes, changing ROMs, achieve orgasm when u improve ur benchmark scores?
if yes, then sgs2 is the better choice.

but shld u want simplicity, smooth and premium experience out of the box, with tons of functionality, then its iphone4 (even though it is 1 year old model).

anything in between then the htc sensation may do well.

also, if u cannot imagine urslf paying up to 2k for a flimsy and plasticy phone, sgs2 is not for you.
bcos of its thin material, u can feel the phone heats up very fast.