Call forwarding

Is the call forwarding can be set in softphone or sip phone instead of doing it in asterisk server? Eg. mobile we normally do it in divert feature instead calling to telco.

Tested 2 softphone using same device number and both are ringing when calling the users. Meaning there are no conflict alert when both devices using same number. Is it like this or can be change from asterisk when got 2 deivce using same number will alert like computer using same IP prompt conflict IP address?

Please advice

Thank you