what apps u have, do have rom manager installed?
use the handsfree if you're going to call for a very long time, its even better, no radiation 

The naturality of human being is to adopt and react to situation.. One day, they realise that the what so called heating issue not only in sgs2 but all the phone, they will invent casing with cooler in the future..so heating problem is normal and can be neglacted as certain country(with temperature below 15 degree c) find this heating issue as advantage..

I have seen a picture of heat produce comparison between sensation and sgs2.. sensation produce more heat but since it have alluminium body(specific heat high) then u find it not hot but the inside u never know...
I remember 1 member posted about the radiation from sgs2 is the smallest and the highest if from iphone 4...

I am not telling u to buy, but for me this is a very good phone, very good tread progress if u need support or advice, very good  developers like pulser(villain rom dev) entertained my request without asking for money  and people didnt see the greatness, they always see the weakness...
 

I agree with what has already been said. If you normally make long calls then any phone also is susceptible to heat due to the prolonged heavy discharging of the battery during a call. Not to mentioned as what Benny said about radiation concerns.

If you are so concerned about heat then think about this - many years ago it was considered trendy to hang your phone around your neck. IMHO it was a bigger concern coz not a lot of people bother to think about radiation concerns placing the phone so close to your heart for an extended period of time.

This solution can be solved by considering the use of a Bluetooth headset. Solution already exist and if you decide to hold back then it a personal choice.