Also, you need to find a great location (read, high rental expense - fixed cost), this is a volume business. Worse, some of the hottest service providers no longer recruit new dealers.
Our business now focus on Prepaid wireless which is booming in the US (saturated in Europe). We have opened an online store which is something you could consider because you can avoid the high fixed rental expense. Prepaid commission ranges from 2% to 20% (but as you can imagine, the higher the commission, the hard to sell because they tend to be too expensive).
I won't provide our online store's link here to avoid being suspected running a commercial here.
Hope this helps.