It’s not only about the subscription price.
Apparently Salt and Sunrise charge for using fast payment systems like Twint, Apple/Google/Samsung Pay, CC, etc. At least Salt does so also for its secondary brands like Post Mobile, Lidl, and GoMo. Salt charges .95, Sunrise 1 CHF.
This looks quite clearly like profit maximising as the subscription prices have gone up in the recent past as well. It doesn’t look like they’re shifting costs onto those who cause them because in this case they’d reduce subscription prices simultaneously.
Market leader Swisscom doesn’t have such a charge (so far). Other providers that use Salt’s or Sunrise’s network (can) have their own policy, Spusu for instance uses the Salt network but has no such charge.
Here’s Tagi in German, unpaywalled:
https://archive.is/20250627052729/https://www.tagesanzeiger.ch/zusatzgebuehren-wie-salt-und-sunrise-ihre-kundschaft-veraergern-122777314353