My this and your this

La hotel in Medan.
- hello, can you hear me?
- yes, sir.
- this is room 309.
- no.
- what do you mean? This IS room 309
- no, sir. This is room service.
- I mean THIS is room 309, the room I'm calling from
- sorry, sir, this is room service. For calling room 309 please dial 8309.