O2, Vodafon, Telekom and Co. collect customer data.
Information such as age or gender is stored by network providers such as O2. It is not uncommon for this data to be resold. Many people don't want that – and it's a topic that falls under data protection. With two providers, an objection is quite simple. You can find out exactly how this works – and who the "grey sheep" among network providers is here. The corresponding service to object to data evaluation or disclosure is called opt-out.