Mobile network state "connected", but not

Nexus S I9020T does not work on mobile network state as "connected". It really works at home and office network on wireless acess points, but not at mobile network operator. This service is provided by the operator and works well on other cell phone, but not at this moment at Nexus S. It use to work well. Can i fix it by by my self or I have to deleaver it to Samsung costumer service?

I do appreciate any help.