Hi, i have a nokia x3 and it won't show the callers name even though they're in my contacts. what do i need to do to rectify this? Thanks!

This could arise as a result of two things.
First thing, if the default contacts are the sim contacts and then there are no contacts stored to the phone memory. You have to set it up to show the sim contacts as the default or phone contact(depending on which memory is having the contacts). Better still, you can copy the contacts from your sim to phone memory.
secondly, since you are sure that it is stored to the phone, and it still doesn't show, it is as a result of storing the contact with two different names. Possibly when you changed the sim into the new phone, it made some changes to the contacts and saved them from your sim to your phone memory. As a result, there are 2 names for one number and the phone cannot pick which to show. The number has to be stored with a particular name both on phone and sim memory.
if you need more information, contact me.