Below are the formal and polite equivalents (synonyms) of 'talk about' or 'speak about' which you can use in your business or professional pieces of writing:
It has exactly the same meaning and uses as 'talk about'. To say that you did it for a long time, add 'at length' after it.
'The question about the cost will be dicussed at length in the next meeting.'
It means to 'talk about' something for a short time and not in a lot of detail.
'I mentioned the need to perform an audit.'
It means to introduce a topic, subject, point and then 'talk about' it.
'You raised some interesting points in your last email.'
It means to introduce a topic, subject, point and then 'talk about' it.
'If there is anything that you would like to be brought up in the next meeting, please let me know.'