Your pricing page is not as clear as it could be.
When people read "$0.001 each" they sometimes understand it to be one thousandth of a cent rather than one thousandth of a dollar.
Even though you are completely correct/accurate, people find it confusing (1).
Wouldn't it be clearer to say "1 cent fore every ten uses" (or "10 calls for a cent" or "a tenth of a penny per call")?
Admittedly, your audience is semi-technical, and should parse it correctly, but why not simplify it?