Actually this is an easy fix if you're willing to root your phone. I had this same annoying pop-up multiple times a day and didn't want to give in to Boost and install it. Especially after the Boost customer service rep told me that "Mobile ID is required for your phone to function properly and you must install it." What a load of BS... Rooting isn't difficult or dangerous (if you follow the instructions), though it most likely will void the warranty on your phone.
Here's what I did. My phone is a Samsung Galaxy Rush, so these instructions reflect that. Check Google for rooting instructions for your specific phone. They should be similar. I got rid of Boost Mobile ID and other annoying bloatware as well.
ROOT THE PHONE
1) Download the three essential files (ClockworkMod Recovery, Odin, and SuperSU) and follow these
rooting instructions. (Again, this is for Galaxy Rush - check Google for instructions for your specific phone.) In summary, ClockworkMod Recovery (also known as CWM) gives you the ability to install programs to your phone from a .zip file on your SD card. Specifically you'll need this to install SuperSU. Odin is a Windows program that puts CWM on your phone. SuperSU is the program that allows root access for selected apps on your phone. So Odin installs CWM and then CWM installs SuperSU. Don't worry about flashing any custom ROMs (step V). It's not needed to resolve this issue.
2) If you're running Android 4.1 (aka Jelly Bean) or later, you'll need an additional step not explained in the link above. That article was written for 4.0 (Ice Cream Sandwich). Jelly Bean is clever-er and will try to replace your newly-installed CWM with the stock recovery app when your phone reboots at step III.13 in the instructions above. So right after Odin tells you that the CWM install has successfully completed and your phone starts to reboot at step III.13, immediately remove the phone battery and unplug the USB cable to prevent that reboot. Then proceed with step IV.2. You're back in business.
3) Proceed with the rest of the steps in the article to root your phone. Once that's completed, it's time to go shopping for free stuff! Open up the Google Play Store on your phone and search for a free app called Uninstall Master. There are other similar apps you can use instead, but Uninstall Master is easy to use and worked well for me. After you install and run it, you'll get a dialog box asking whether this app can have root privileges. Grant this privilege because the app will need it to remove your bloatware.
DELETE MOBILE ID AND OTHER BLOATWARE
4) In Uninstall Master, slide over to the System Apps tab. You can delete any app on the phone (even really important ones so be careful!). Look for Mobile ID app in the list and delete it. I also deleted a bunch of other stuff I don't need like Boost Zone, Google+, and Facebook. By default, Uninstall Master will just move these apps to a recycle bin instead of really getting rid of them. That way you can bring something back if you later determine you needed it after all. I recommend always using the recycle bin feature just to be safe.
Hope this helps.
Facebook
Twitter
Instagram