While you would not write " Jennifer speaking " on a sticky note, you would not say "Jennifer is speaking, " on the phone. Language is adaptable.

A single dose may have have multiple milligrams of any product, the dosage is identical for each dose.
Three different vaccines were formulated with different dosages of any particular to provide immunity to a human body against the same virus. The dosage of each vaccine may also refer to the number of required doses to complete the vaccination. If each dose of ibuprofen tablet is 200mg. You must take 4 doses ( or 4 pills ) to reach the same dosage of active ingredients found in a single dose of an 800mg ibuprofen tablet.

I agree, it makes no sense. However, so does "contacting" someone or a company for the first time unless one or it was listed as a contact. An introductory sentence should have "you" as the subject, a verb of action describing "your way of communication", and complement spelling out the reason for "your correspondence". For example, " I am writing to inquire about the new position", " I am emailing you my resume, " I am submitting my online application for the position". Verbs describing the sense of the correspondence, such as "I am sending you my contact information" " I am responding to your job offer", or "the reason I am calling is to ask if/for/about, though, asking directly is just as good, on the phone, but not if you are sending a telegram, unless, it's an SOS, a text or other type of message alert. The radio always says what you are listening to", the television always thanks you for watching, a contact for meeting, a person for inquiring, responding. If one feels they were reaching out to you, thanking them for doing so is all you have to do, as your focus should be entirely on the fact that they did.