Privacy implications of an employer provided SIM card in a personal phone

The question about what an employer can see on an employer provided cell phone has been done to death on this sub. Both when an employer is and isn't using Mobile Device Management.

I have a slightly different question: what are the privacy implications of an employer provided SIM card in one's personal phone (for those of us who can manage dual SIMs and thus have a personal and work number in a single device).

I'm under the impression that …

card employer personal phone privacy sim