I pay HKD298 (US$39) per month to SmarTone for 1,400 basic minutes with 600 intra minutes and unlimited data with tethering. (full plan)
For the amount of minutes I get with SmarTone, I’d have to get “Nation Unlimited” on AT&T for US$69.99/mo. The closest data option AT&T has is “DataPro 5GB for iPhone 4S Personal Hotspot” for US$50.00/mo. One thing that AT&T includes that SmarTone customers have to pay HKD18/mo for though is visual voicemail. (full plan)
Not including SMS/MMS, I pay about 1/3 on SmarTone of what I would pay for a similar plan on AT&T – $40.75/mo vs $119.99/mo, respectively. Plus I get more bars and cool features like X-Power.