I wouldn't say it's related in any way to the alphabet in use. Take the English 'a' as an example: skate and car produce two different sounds out of the same letter.
Alphabets transmit words, much less so sounds.
Alphabets transmit words, much less so sounds.
A and Å are different letters, and can't be substituted for each other.
In English, that is. Some languages using latin script always use the same sound for the same letter (how it should be done, IMHO).