Distinctive Ringtone issue

i have asterisk running in my company and i’m using TDM400 for the 3 analog lines i’m using.
i want to do the following:
when there is an incoming call to any user i want asterisk 2 send a distinctive ring tone to the phone which is used by the user so that the user can distinguish if this call is from inside the company or from outside through analog lines or it is a transferred call (through the ring tone produced by the phone).
is there any idea about how can i do that?
thank you so much