I upgraded from an iPhone 5 to XS. the 5 had a mobile-carrier company sim card (non-apple). To save phonecalls, I just plugged in the old sim card into new phone and it worked. I think the new phone has a apple sim card. The sim card that came with the new phone looks newer and more shiny. Are there any disadvantages of sticking with the old sim card? Everything seems like it works. I was just wondering because many but one android user sent me an text message and it didn't go through. The 5 underwent submersion but the water damage detector didn't register water damage.
In terms of using the phone day to day, there's no disadvantages with re-using the SIM card from the old phone.
The disadvantage lies primarily with the fact that if you had requested a new SIM card from your provider, you would have received one that could be running newer software (inside the SIM card). This could be relevant if you were the target of a specific hacking attempt, as the SIM card software is rarely, if at all, updated by providers after it is sent out.