GTS-LUM is a user behavior model that reshapes modeling paradigms in the telecommunication industry.It employs a (multi-modal) encoder-adapter-LLM decoder architecture and telecom-specific innovations.GTS-LUM supports diverse time granularities, multi-modal data inputs, and aligning semantic information with behavior data.Experiments validate the effectiveness of GTS-LUM, which outperforms LLM4Rec approaches in user behavior modeling in telecommunications.