How Do I get internet service on my PSP?

I bought a used PSP 3000, the last version before Sony made the GO download game version and a 4 GB memory stick but I can’t connect to the internet…it keeps trying to use T-Mobile as a service…How do I get online service to browse the internet and play others online…what do I have to do and how do I register it with Sony Online?

go to infrastructure mode then search for your internet… then again, it might be different from what i have