Do you mean the key for the wireless internet access ?
Hello,

let's say I phone with someone and he asks me for a key but I dont know what kind of key he means.

So I ask him..
"Do you mean the key for the wireless internet access or do you mean the key of my house?"

Is it correct to say that?
Im particulary interested in the preposition "for".

Thanks in advance!

Question

Do you mean the key for the wireless internet access ?
Hello,

let's say I phone with someone and he asks me for a key but I dont know what kind of key he means.

So I ask him..
"Do you mean the key for the wireless internet access or do you mean the key of my house?"

Is it correct to say that? 
Im particulary interested in the preposition "for".

Thanks in advance!

Answer

You would ask "Do you mean the key to my house or the key(or code) for the internet?"

Also, you do not "phone with someone"
You speak/talk on the phone with someone

Answer

These prepositions are all correct:
"key of my house"
"key for my house"
"key to my house"