Picking-up an English accent (British, American, etc.) in one of the most difficult things to do, since you have often have to train your vocal cords on pronouncing phoneme that are not natural to your mother tongue.
Having to practice your voice and your tongue would be hard because it would be unnatural. I think with practice, it could still be done, just like British actors doing American accents, etc.
Speaking English regularly is part of the path to improve pronunciation, but more often than not, that is not on the day-to-day agenda.
I think this is the one that needs to be done. If you want to really practice, doing it every day would make your progress much faster.
However, I mentioned in a much narrower range, in the forum, people don't need to speak (actually the bitcointalk.org has not had features like livestreaming, etc. so far) so the first two important things for members whom want to improve their English and communicate better in the forum are: Reading and Writing.
Don't you think that once you have learned how to write, you wouldn't get to speak? Speaking and communicating with someone who is good at it could help you develop the consistency that is needed for you to be efficient in English. The big effective reason that I could think about when doing this method is that you are hitting two birds with one stone. Speaking, like how you are going to communicate IRL and forming thoughts like in writing instantaneously.
Did I saw only applicable to a mobile phone? (how about on laptop?).
I think it works with a laptop too, knowing that it also has a mic. There are some software examples but I haven't tried it all the way. Mobile phones are like everywhere and most people have it, that's why I think it's necessary that I focus on that one.
Be careful, using the phone while driving "even if you use this method" is illegal and may expose you to accidents.
Duolingo & Grammarly will give you better results.
You shouldn't really use your phone. I'm doing it handsfree, so I could keep my eyes on the road every time.
I haven't tried Duolingo but I saw it has good reviews learning a different language.