check out resco contact manager, i use that for my palm treo pro and it has the ability to handle calls. And as such there is an option for full screen contact picture for caller id.

Also resco contact manager has got to be one of the best contact managers available for windows mobile. Full touchscreen support and very finger friendly, different views that make it easy to navigate contacts, can handle missed calls and sms as well as contacts, can grab facebook information to update your contact list!

check it out, they have a trial, so if its not what you are looking for you dont need to buy it.

http://www.resco.net/pocketpc/contactmanager/

p.s. pm me for more information regarding the download