Using different Apple IDs for device and iTunes Store
If you mean a different Apple ID for iCloud services and iTunes, yes, that is possible. On iOS, your iCloud login is in Settings / iCloud and your iTunes login is under Settings / iTunes Store and Apps. On OS X, your iTunes login is in iTunes under the Store menu, and iCloud is under System Preferences / iCloud.

Note that the iCloud login is tied to your iCloud account, your icloud.com/me.com/mac.com email address, and other services. If you are actively using that email address, you may not be able to switch to the Apple ID you use in iTunes.

Apple does not currently provide a way to merge Apple IDs.