Inspiration and Where to Draw the Line

Just something I was thinking about today - where does one draw the line between being inspired by another design and borrowing too much from it. The reason I'm thinking about this is because my design ended up being influenced greatly by Docomo's ad:

Here's my design (in the works):

I'm not sure to go with the original, without the blocked letters, even though I like the block style. Anyway, just some random thoughts about design.