The IMEI number within the phone settings should match the IMEI number behind the battery on the back of your phone.
This will not change granted you do not route or unlock the phone to other networks.
If you are worried about your phone you can have it looked at by a Samsung engineer, there are two options for this;
Firstly you can take it to a local service centre, find your nearest one by clicking on the link below;http://www.samsung.com/uk/support/l...
Or you can arrange for it to be posted to use by calling our Galaxy Team on 0330 726 7864.