hidden caller id leaks.

m4ri0g

by default, the first thing i do when i get a new phone or a new sim is go to call settings and disable caller-id from network default to do not send my caller id.

i have notice that if i call my work number (a sim card provided by my employer), it always displays the number but if i call an other personal number.. it is shown as unknown caller.

is it a feature enable on the sim card that will no matter what display the call id? it means even if i choose to hide my number it is still being sent.
i do not know how cellular works to be honest but i am perplex and eager to understand why?

thank you.

ve3jlg

m4ri0g
It could be that your employer's number is using ANI, which is a separate calling number identification from caller ID. Does you employer have a 1-8xx toll free number?

I discovered that if I call my city's 311 number they get my number even if it is blocked. They also have a 10-digit ordinary number and I learned recently that they also receive my number when I call that.

"ANI is conceptually and technically different from caller ID service.[1] A caller's telephone number and line type are captured by ANI service even if caller ID blocking is activated. The destination telephone company switching office can relay the originating telephone number to ANI delivery services subscribers. Toll-free subscribers and large companies normally have access to ANI, either instantly via installed equipment, or from a monthly billing statement."
https://en.wikipedia.org/wiki/Automatic_number_identification