I use two phones one is quite old k500 (always connected to computer..) and w810i.. On k500 there is not option to save user birthdays with contact so I write down dates in "info" field for each user.. On w810 and newer models Of course I use birthday field as expected.. I wonder could u add option that will do following thing.. When I try to copy contact from newer phone model (like w810 which have birthday field) to old phone model (like k500 or anyone else which does not have birthday field) MPE check and if old model detected (no birthday field) it will append birthday date into "info" field like "birthday: 31.12.1980." following with text previously entered in "info" field.. That could be added as option we could choose just before paste is done..like "Birthday field on destionation phone does not exist! would u like to paste birthday in info filed on destionation phone? Note: After synchonization with {OldPhoneName} PIM managers will NOT include birthday info".. that's all..If someone come up with better idea, feel free to share it here..
10q
I must said I hear before thing "I'm the boss" answer.. I'm not dissappointed with rejecting solution but the way u sounds.. sometimes I think u r here to scare somebody not to feel and get to know what your consumers says.. but as u said u r the boss.. 
peace..