You can change providers, while still keeping your old number. This is referred to as number portability. Number portability is available for switching mobile providers as well as for fixed net providers. For fixed net, however, it is only necessary if you completely change providers, i.e. if you change to Cablecom or a VoIP provider, but not if you switch to a Preselectionprovider such as Sunrise or Tele2. The new provider may choose whether or not to offer number portability for new customers. Certain cheap deals such as Aldi do not offer number portability.