If one doesn't need data plan, then just go buy a cheap phone anywhere. Then go get a prepaid card that usually starts at HK$48. You can compare all the plans on the respective carrier's website for prepaid card - 3, Smartone, 1010/CSL, PCCW/HKT, China Mobile. And there are cheaper ones like New World. There are various cards - some cheaper for local calls, some cheaper for international - so, it depends on where you need to call.

AND if you're really frugal, then you can also go to some downscale malls to find shops that sell various cards at a discount (compared to if you go to 3 or CSL's own shops). OR they will also be helpful if you want to choose your number.

Really, for just calling and no data, no reason to get a contract. But having said that, having data is invaluable in Hong Kong. After I moved back from the US (with no data plan and no smart phone), first thing I did was to get an iPhone with data plan. One spends so much time on buses/trains away from computer a day, it's very helpful to look at bus schedules (and real time arrival time), maps, train arrival times, restaurant info, etc..., not to mention connecting with friends while commuting.