iPhone 5c No Modem Firmware BUT …

iPhone 5c No Modem Firmware BUT … there is IMEI … !!! After Restart there is singnal 3g i can call and receive calls … but after a while , maybe 10-15 hours the MODEM FIRMWARE disappear , the signal bar is still full and showing the Carrier I take out the sim card to reinsert it but when i pull out the SIM card the signal bar and carrier is still there …. when i insert the sim , the signal bars are not moving and i cannot call my number from another phone its says that the phone is out of network coverage .. is this a baseband chip or some cap is shorted ?