i have the same problem. it happened 3 days ago. i've done everything. reset, upgrade, sim in sim out, all the thing that i can possibly do by my self...
finally i went to apple service centre. they said it is about a hardware issue. they should change one part of the chip in the firmware. it costs 120 USD to fix it. and my iphone has to stay there for 2 days...
so in my experience theres nothing to do except ask someone to replace the chip.
i have iphone 5 with ios 8.3.
Thanks.
Lisa