A windows phone SMS/MMS backup viewer/ Microsoft has provided a free contacts+messages backup utilities since Windows Phone 8.1. Unfortunately if you have had SMS backup turned on, at the same time change your phone, get new SIM cards, all the information will be messed up. One example is the duplicated information / text messages, and broken group messages chains. And, not to mention corrupted restore process for large backup.
This utilities is to help view the messages / contacts backup files in PC.
I still have no clue how to regenerate the backup package so they can be properly restored. Give us a shout if you know how to do it.