First off are you getting your own phone? if so then if the data in question ,like photos, are on a SD card in the phone instead of it’s internal memory you should be fine. You can always pull the card and load them to the new phone. By mentioning your own plan, is this going to be a new phone and/or new provider ?
Your data will not be removed. Just simply copy all your data to the itunes account by connecting it to PC. Now, disconnect your phone and connect other phone. Now, copy your data from itunes to other phone. Your data will remain safe.