SCO Open Server 5

A program that I am working with outputs data to a system or printer with the traditional output
> lp [-options] [system-printer]

This output line along with some other job output formatting information is stored as a defined output within the program so that the average user scrolls the list of defined outputs, such as, HPLaser1, and the corresponding settings and destination are handled.

I am working with a fax package for the system which, in the majestic simplicity of UNIX, works much the same as above. The output sequence is
> fax [-options] [phone-number]

again..

> fax -a -t 5551212

This is great for setting up as a standard destination within the program as long as the user always wants to select "FAX-Office2", knowing that the output always needs to go to the fax machine in office2 with the phone number 5551212.

How can I create an output sequence that would prompt the user to input the destination digits? The goal is for the user to select "OutboundFAX"... Which is already defined as a destination in the software of

> fax -a -t [prompt user for destination phone number]

System would respond:
"Please enter fax phone number"
?

After receiving input, system would proceed

> fax -a -t uservariable

Thanks,