Guide: Expenses you should not forget as a Swiss freelancer
A comprehensive list of all the expenses that you should think of in preparation for your tax return to make sure you pay the least taxes possible.
As a self-employed, you probably use your phone to do business calls and use 3G and 4G for business communications (such as creating invoices for example).
You can therefore expense a percentage of your monthly phone subscription (Swisscom, Salt, Yallo, Sunrise, ...). It is your responsability to compute what % of your usage of the subscription is professional vs private.
20% is a reasonable estimate for most situations.