If he maxed out his time with 60+30 days on both entries, it might raise some suspiciouns.
But if he didn't, and also went back home and spent a significant time back home in between visits he will likely fit the pattern of a actual tourist and it will not be a problem.
He could just apply for a tourist visa too, if he is worried.
I have had my pre-paid number since around December 2021.
Same number, it has never changed.
Even bought it at the airport initially.
If you top it up regularly, you keep the number.
And I bet you a dollar that most bank branches will be fine with pre-paid SIMs. You can get proof of ownership of the number from your local operator shop quite easily. If required.
I have opened all of my accounts with a pre-paid SIM.
Last ones around 3 months ago.
But even if you did in fact genuinely need that, you will need to go to Immigration for a Residence Certificate to open a bank account anyway, so I don't really see the problem here. Just get both of at the same time.
Some offices give them out the same day as the application. Mileage will vary on that.