Someone recently asked me why the letter 'o' is pronounced as /ʌ/ in so many words of English: come, company, some, done, money, monkey, dove, love, above. Why are these words not spelled with 'u'?
The answer is this: in cursive handwriting, the sequences 'um', 'un' and 'uv' are rather difficult to decipher, because there are so many short vertical lines occurring one after another. As a result, scribes preferred to use 'o' rather than 'u' before 'm', 'n' and 'v'. Note that there is no such problem before letters such as 's' or 'p', which is why words like must and cup have the expected 'u'.
The only words that don't fit into this pattern involve 'o' before 'th': other, nothing, mother, brother, smother, etc. I don't know why 'o' rather than 'u' occurs in these words.
One other observation: in Brunei, there is a tendency for spelling pronunciation to occur, and about half of UBD undergraduates have /ɒ/ rather than /ʌ/ in the first syllable of company. I don't know how many other words have this kind of spelling pronunciation.
In fact, this shift is also found in some words in Britain: about 30% of people in Britain now have /ɒ/ rather than the traditional /ʌ/ in one, and this trend is strongest among the younger generation, suggesting it will one day become the norm. Furthermore, Coventry once had /ʌ/ in its first syllable but it usually now has /ɒ/, and covert used to be /kʌvət/ but 46% of people in Britain now have /əʊ/ in the first syllable of this word.
It seems that spelling pronunciation is widespread, and places like Brunei may be leading the way in this respect!
(All percentages for British English above are from: Wells, J. C. (2008). Longman Pronunciation Dictionary (3rd ed.). Harlow: Longman. The data about UBD undergraduates is from page 41 of: Deterding, D, & Salbrina, S. (2013). Brunei English: A New Variety in a Multilingual Society. Dordrecht: Springer. The observation that scribes avoided 'u' before 'm', 'n' and 'v' is from page 118 of: Algeo, J. (2010). The Origins and Development of the English Language (6th ed.). USA: Wadsworth Cengage.)