I could see abusing the dial as a potential arc for Nelson. Like drugs or steroids it allows him the opportunity to escape his out of shape self and transform into a strong and powerful completely different person.
Some of this is fixed by the fact that not every hero he turns into will be one he likes, also the fact that it runs out after a couple hours means he can't choose to stay that way permanently.
Also, having the dial in a public phone offers the possibility to have others stumble on it for 1-off stories along the way. Or what happens if somebody finds it and starts using can the dial affect multiple people at the same time, or would Nelson have to wait for it to wear off on the first guy before he'd have a chance to use it.
I don't know why I followed it up with a lot of guesses towards the future instead of simply enjoying what we have so far. It's a great title.