I found most of niches almost right away. Three of them are related to eBay and Amazon products that I sell and the rest happened because they are hobbies/interests of mine. This makes it extremely important for writing my own articles as the subject matter I could talk about endlessly. If you feel that passionate about the mobile phone market and devices in particular, then go for it. Instead, due to the high competition of that broad niche, narrow it down and really focus on differentiating your content.
For instance, if you like a particular Samsung phone on the market now, get info on the NEXT phone coming out and so on. Create a buzz about products that have not even launched yet so that by the time that they do, you are already established and starting to rank. Mobile phone market changes way too quickly for my taste so I wouldn't touch technology like that. Many gizmo and gadget geeks already have their preferred sources when it comes to finding product info so you will have a difficult time making money here.
The other trick to finding a lucrative niche is to decide first how you plan to make money from it. Do you want tons of traffic and just a few measly Adsense clicks? Are you selling these products or affiliate marketing for these products? Will you be creating a community of subscribers that you can directly target with offers related to your niche? Maybe you want to make money with all three of the methods I just described (I do this on most of my niches).
Set yourself a goal in IM so you know which direction you will be headed and start to take action. This is the best advice I can offer. If you find that a particular niche is giving you difficulty, then you know that you will have to change gears and pick something else. Better yet, make difficult projects long term ones that you slowly add to over time while you focus on smaller niches that will offer quick returns.
