No need to worry grahamsthe1! VZW help is now on the scene to get this resolved. How long has this occured? Have you recently downloaded any third party applications? Have you attempted to remove and reinsert the battery? Please keep us posted, thanks!
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I have been having this problem with my S4 Mini. I will be mid-phone call and it just shuts down, doesn't matter if I received or initiated the call. Sometimes if I take out the battery for a few minutes before the call and keep it short then I can get through it, but most of the time it doesn't work. I tried making a post on the forums but no one responded, there never seem to be chat agents available and I can't call, the phone will just shut off in the middle of it. Please help.