Newest iPhone update is linking calls between two phones.

Let's break it down and elaborate further:

1. Voice Call History and Voicemail being SIM-dependent: Each device stores its voice call history and voicemail based on the SIM card used. Therefore, if you have two devices with different SIM cards, their call histories and voicemails will not synchronize or be the same. The SIM card essentially acts as the repository for this data.
2. Apple ID dissimilarity affecting FaceTime call history: FaceTime call history is linked to your Apple ID. If you're using different Apple IDs on two devices, their FaceTime call histories won't sync. Each device maintains its own log of FaceTime calls based on the respective Apple ID used.
3. Separation of sharing features from call-related data: Sharing features like sharing pictures, contacts, and music aren't interlinked with call history, voicemail, or FaceTime records. These sharing functionalities operate independently of the SIM card or Apple ID association. Hence, while you can easily share various media or contact information between devices, call-related data remains specific to each device due to its SIM or Apple ID association.

This separation means that even if you're seamlessly transferring photos, contacts, or songs between devices, the call history, voicemail, and FaceTime records will remain distinct and exclusive to each device based on the SIM card and Apple ID used.

Moreover...

Contacts are not stored directly on your device, read my old post --> contacts - Apple Community (Apple Recommended)