[arthurus]

The pronunciation within the Moslem world varies with accent. Vowels are mutable and Maslama is the same word as Muslim in a different regional accent or even a different language. The language is mostly Arabic but there is a large Urdu population and other languages withing the Moslem cocoon. It is further complicated in the Arabic transliteration by the fact that few sounds in Arabic actually match sounds in European and other languages so no transliteration is "correct."
For the name we usually see spelled as Mohammed, Mahomet and Mehmet, and Mahmoud and Mahamdi are also correct. In Arabic the name is spelled (in Arabic letters, though) MHMD. The number and the sound of the vowels changes with the dialect.

[disndat]

This sounds somewhat like trying to decipher Egyptian hieroglyphs. No one knows for sure what the vowel(s) sounds were/are in their language. Except maybe for cases of pronunciations of Egyptian names or places in other languages of the time.