Improving one's grammar invariably moves one's accent closer to Standard English and mitigates the unintelligibility of the ghetto or swamp accent. To improve your grammar you have to begin to think a bit about what you are saying and you will be conscious that what you are doing is trying to be understood by people beyond your old neighborhood. You can't help improving your accent when you set out to improve just your grammar.
Than,
Just not buying it... accent and GRAMMAR are not the same. There are people with incredibly thick accents that speak proper english grammar.
What is going on in the inner city "thug" communities is not even an attempt at english grammar, absolutely abysmal enunciation and frankly vocabularies that are well under 600 words.