Maxcom MM41D User Manual page 23

The phone provides some talk control functions in the
process of call.
During the call, press [DEL/BACK key] to back to Home
status.
During the call, press [Left soft key] to enter [Options]
menu to access the talk control functions.
Hold/Resume talk state
If network supports, you can hold current call.
During the call, press [Left soft key] and select [Hold] in
the [Options] menu.
To activate held talk, Press [Left soft key] and select
[ Unhold] in the [Options] menu.
Dial second number
During a call you can dial another number.
Press [Left soft key] and select [Add call] to dial second
call,
When the second number is put through, the first call will
be held automatically.
Answering a second incoming call