A common scenario for receptionist phones is having the ability to perform a one button transfer to an external number (i.e. transferring a call to the on call mechanic).
Configure a MPK/VPK button as type 'Speed Dial via Active Account' and set the external number you want the call to be transferred to (Settings > Programmable Keys > Virtual-Purpose Keys):
Enable the 'Transfer via Non-Transfer MPK' option (Settings > Programmable Keys > Virtual-Purpose Keys Settings > Enable Transfer via Non-Transfer MPK):
Enable Transfer via Non-Transfer MPK setting is not currently available in GDMS as of writing however you can use the P Code Value for this setting.