Hello I have a 2002 Camry 4 cyl how often should the belts be serviced ?

If you have gotten 100K out of any belts, I would schedule them for replacement. Do you have any besides the main serpentine belt? I am not familiar with your car but most vehicles have moved away from multiple belts in favor of a single belt that is routed around to all components that need belt driven power (AC, Alternator, water pump, power steering and maybe a non-electric cooling fan). As for the timing chain, follow the manufacturer's recommendation. If that breaks, it will quickly trash your engine. Not cheap but very necessary.