They're resilient to spam, but often impossible to recover.
I had a spare SIM card that friends and family use when visiting from abroad. It's been unused for 90 days and has been deactivated. The number is lost, and irrecoverable. A friend had created a (second) Signal account with this number and can no longer log into new devices.
As a more mundane example: If I accidentally drop my phone into a river, the SIM is gone forever, and so is that line.
Sure, you can have a contract line which allows recovery. Depending on where you live, these can be several times more expensive than a regular pre-paid line.
You don't need a "contract" for recovery, just an account.
E.g. in the US, Mint Mobile is $15/mo. and is prepaid in the sense that you buy blocks of months at a time. But if you lose your SIM they'll still send you another one with the same phone number.
So no, if you lose your SIM you don't necessarily lose your number, even if it's prepaid. That only happens if you're buying your SIM as an "anonymous" one-off purchase, which is not what most people do these days. Not to mention the increasing prevalence of eSIMs.
"Often impossible"? Not my experience at all. Maybe it would be more problematic with prepaid SIMs, but why would a monthly billed account get deactivated?
You lose your SIM? You go to a branch, verify your identity, and get a fresh new SIM for your line. There's no more straightforward and surefire way to recover any other type of account as of today.
No. I believe that it's way easier to recover your phone number when you lose your SIM or change your phone (eSIM). When you lose your email password and the recovery code at the same time, your email is gone, forever. That's a huge difference, IMO.
Yeah, it may not work when you buy a prepaid SIM and decide not to use it for a long time, but for billed plans, it's impossible. I've been using the same cellphone number for the last 23 years. I'd got my phone stolen, I was able to reactivate my cell the same day with another phone.
I had a spare SIM card that friends and family use when visiting from abroad. It's been unused for 90 days and has been deactivated. The number is lost, and irrecoverable. A friend had created a (second) Signal account with this number and can no longer log into new devices.
As a more mundane example: If I accidentally drop my phone into a river, the SIM is gone forever, and so is that line.
Sure, you can have a contract line which allows recovery. Depending on where you live, these can be several times more expensive than a regular pre-paid line.