puzzle with cell phone antennas spcace

hi guys,
i am so puzzle with cell phone antennas spcace,and i have some questions as below:
1.for GSM900/DCS1800 cell phone, how cubage is the ideal space of anntnas?(L*W*H)

2.for new projects,ie GSM900/DCS1800(Power GSM=30.0dbm, DCS=29.5dbm and sensitivety=-108),how to evaluate this antennas space without simulator software;

3.for cell phone ,which factors that effect antennas perfermace we need to consider?

Pls explain by monopole and Pifa antennas ,Tks

well,i'll upload one material that can give you some help.