I've kept my first US card for three or four years now, spending $3 per month on it. The phone number cost me $20 to purchase from Numberbarn, then I transferred it to the card. The card itself cost me around 120 RMB. Currently, many new/unopened cards like this one are getting blocked, but older accounts are doing better. You can apply to change your phone number once per year, but the number I bought definitely won't be changed.

My second UK card has been around for one or two years. This card number is random, the card isn't expensive—around 20 RMB—and after topping up with ten pounds, it can be used for 20 years, so there's basically no maintenance cost. You can also directly buy a ready-made physical SIM card for 120 RMB, and the number can be changed twice. I previously registered a Telegram account that got sealed, so I just swapped the number.

Maintaining some overseas phone cards eliminates all the hassles of overseas registration. I think it's quite worthwhile.