With 'Targeting By Carrier' you can specify any mobile carrier you like your campaign to be shown against. This gives you the ability to filter more accurately and improve optimization of your mobile campaigns.
Important Carriers for Germany
Selecting Mobile Carriers
Select a campaign, click 'Edit' and choose 'Traffic Targeting / Filters'. Turn on 'Targeting By Carrier' and select the items of your choice. Save your settings.
If this targeting option is not active or no option is selected, the campaign is automatically shown on all carriers.