Can't iMessage certain iPhone users

[Jack D.]

I don't know if this translates to imessages but I had a similar issue on an android phone. I had 2 people in my contacts list that could call me but when I called them it would go straight to voice mail. The fix that worked was to delete them and me from our respective contacts lists and then reboot. Then they called me and we added each other to contacts again and all was well. YMMV.