Yealink SIP-T48G - Why does the IP phone play the local ringback tone instead of media when placing a long distance number without plus 0?; Wireless Issues; Why is the wireless signal strength low?; Upgrading Issues

Administrator’s Guide for SIP-T2 Series/T19(P) E2/T4 Series/CP860 IP Phones
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Ensure that the 180 ring workaround feature is disabled. For more information, refer to
180 Ring Workaround on page 290.
Ensure the SIP-T48G IP phone and your gateway/ router are within the working range
and there is no obvious interference (walls, doors, etc) between them.
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Do one of the following:
 Ensure that the target firmware is not the same as the current firmware.
 Ensure that the target firmware is applicable to the IP phone model.
 Ensure that the current or the target firmware is not protected.
 Ensure that the power is on and the network is available in the process of
upgrading.
 Ensure that the web browser is not closed or refreshed when upgrading firmware
via web user interface.
Press the OK/√ key when the IP phone is idle to check the firmware version. For example:
44.80.0.60.