You will get a network that has a contract with your operator. The roaming regulations basically require the foreign networks to meet all reasonable requests for roaming: http://berec.europa.eu/eng/document_register/subject_matter/...
> I wonder if it would make sense to get a contract in another country, so that I can use all networks in Germany for free?
There are fair use clauses that allow the operators to charge for permanent roaming: http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A3... (section 3)
You will get a network that has a contract with your operator. The roaming regulations basically require the foreign networks to meet all reasonable requests for roaming: http://berec.europa.eu/eng/document_register/subject_matter/...
> I wonder if it would make sense to get a contract in another country, so that I can use all networks in Germany for free?
There are fair use clauses that allow the operators to charge for permanent roaming: http://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX%3A3... (section 3)