Question about digitec connect SIM card for mobile subscription

Sure, that's possible🙂 I quote from the help centre:
"Yes, you can of course keep your existing number. In the registration process we will ask you if you want a subscription with a new number or if you want to keep your current number.
But make sure you buy this special offer, then you'll only pay the equivalent of 15 francs/month instead of 25 francs/month for the first year.