I am a caller at every home...

I am a caller at every home where you may meet, For daily I perambulate along each street. Take one letter from me and still you will see. I’m the same as before, as I’ll always be, Take two letters from me, or three or four. I’ll still be the same as I was before. In fact, I can tell you that all my letters you may take, Yet of me nothing else can you make.