87
SIM failed
1.
The SIM card is
dirty. Clean it.
2.
Reinstall the SIM
card.
3.
The SIM card is
damaged. Replace
it.
Poor signals
Check the signal strength
icon on the screen. If the
icon contains 4 bars, it
indicates the signal is the
strongest; if below 1 bars, it
indicates the signal is very
poor.