Sony Ericsson GR47/GR48 Integrator's Manual page 27

Turning the Radio Device Off
LZT 123 7589 R1A
5. SYSTEM CONNECTOR INTERFACE
ON/OFF
VIO
Figure 5.3 Off timings and VIO performance
(2) It is a requirement from most GSM network providers that GSM products
properly detach from the network during a power-down sequence. In
order to achieve this it is important that the VCC supply is not removed or
turned off before VIO has been deactivated by the module.
t
OFF
t
PULSE
t
SPD
27