Finally! A Solution for "Data Call Failure" or Error 67
First of all, proceed at your own risk. Poking around in your phone can cause problems if you're not careful.
I'm posting this because I spent quite a bit of time searching, but could find nothing that worked. I tried resets, updating profile/PRL, etc and none of them helped. I finally bit the bullet and called Sprint. After a short discussion about everything I had tried, a nice lady named Rachel had me update my data profile, which is apparently different than resetting it. You need to get into the SCRTN menu and the required EPST code is ##72786#, which is one that I did lot have in my handy list of useful codes.
After entering the code, you are presented with a password prompt, which is where you input your MSL.
After doing so, you are at the SCRTN main menu.
When you tap "Menu" in the upper right hand corner, one of the two options presented is "Reset".
Tap that bad boy and you get this confirmation message.
When you tap ok, it does it's thing and then reboots. When it finishes rebooting, it should start the handsfree activation process and then all will be right with the world....or at least it was for me.