Customers with older subscriptions (german only) which are no longer sold can retain those. In most cases, however, the new rate plans offer more advantages. It is not possible to renew a contract under an older rate plan. With all older rate plans, a switch to one of the new Sunrise Freedom subscriptions is necessary when purchasing new hardware with a hardware plan.
You can switch a subscription directly in My Sunrise. There, you can see all subscriptions available to you.