In American English, we would say "I'm on 30th Street." I am assuming that the street name is "30th Street". I live on "South Plain Road". This is an example conversation that I might have with a friend of mine. Sara: What are you up to right now? Me: I'm shopping downtown. Sara: Do you want to meet up for coffee? Me: Sure. Sara: Ok. I can meet you. Where are you at right now? Me: I'm on South Plain Road. Do you know where it is? Sara: Yes. Are you closer to the town common? Me: Yes. Sara: Okay. I'll meet you there in five minutes.

I'm assuming you mean the number of the street. If so, it would most likely be: I am at 30th street or I am on 30th street.