How to get Caller Id in PPP

hello
I am workin with PPP to send data from dos machine to unix & Linux machine using FTP with help of fax & voice modem(Caller id Enabled & Exchange provides facility). i need to identify phone(number) connect with Dos machine i.e. to identify from where data is send. so i want to get the phone number. can anybody tellme how to get the callerid in unix/linux machine using PPP?