Ahh - you want to know the "magic trick"...
To park a call from a phone, you invoke the blind transfer (
## by default) followed by the parking lot extension (
70 by default). In case there are some extra dial plan entries that start with the parking lot extension, you can tell the system that the extension dialing is complete by pressing pound (
#) after the extension number.
To configure a programmable key on the Yealink phone that sends calls to the parking lot, you should therefore create a speed dial entry with the digits
##70#
When you press this speed dial button while on call, the phone will dial these DTMF digits - Asterisk will interpret them as a blind transfer to the extension 70 (parking lot) - the call will be parked and the parking lot extension will be announced on the Yealink phone.
To program a button that transfers a call directly to a specific mailbox, you should do pretty much the same - blind transfer (
##) followed by voicemail direct dial prefix (
#* by default) followed by the extension number (e.g.,
221) and finally by pound (
#). The speed dial for transfer calls to mailbox 221 would therefore be
###*221#