PoW = Proof of Work
The proof-of-work system/protocol which is used by Namecoin, was first used in the mid-1990's for fighting spam emails. The idea never found a truly useful cause until 2009 when bitcoin was created. Bitcoin itself utilizes this protocol in its transaction blockchain and thanks to this we can witness the growth in bitcoin mining.
The base idea of this lies in a challenge and proof (or response). The challenge is a transaction, which is a specific cryptographic puzzle. The proof is that a miners computer cracks the puzzle, so the transaction goes through. And that is proof of the miners' work and him providing his hardware for the validation of transactions. The more hash power a miner can provide for validating transactions, the bigger his Namecoin reward for the service is.
The problem with PoW is that mining has become so large that miners are investing into giant A.S.I.C. hardware which is highly energy consuming. Many mining farms are built around the globe as bitcoin has risen in value.
The Namecoin block is mined every ASIC. But this block is then divided between all miners. How long does it take to mine 1 block of Namecoin for yourself depends on your hash rate, which is basically how powerful your mining setup is. For mining Namecoin you will get the best results with using gpu.
It is difficult to say how much does it cost to mine 1 block of Namecoin because it depends on the price of your electricity. But in general, if you want to be profitable, you have to invest in specialized mining setups called ASIC. They are created for mining cryptocurrencies, and because of that, they have perfect parameters for this job together with high efficiency.
Although it is entirely possible to mine Namecoin on your computer, you should consider investing in the ASIC mining setup if you are serious about cryptocurrency mining. Actually, the best way how to mine Namecoin is the gpu. Anyway, if you really want to go with the computer way, try to join some miner pool.
In the beginning, you can try mining Namecoin at home with your computer. Once you get more experienced in mining, you can invest in gpu. That is the best way how to mine Namecoin. But make sure to check mining profitability charts, so you are not just burning money.
Mining Namecoin on Android is straightforward. All you need to do is install an application called MinerGate. After you have installed it from Google Play Store, create an account, and you are ready to mine Namecoin on your Android.
Unfortunately, it's not possible to mine Namecoin on iPhone. Apple restricts it because mining caused damage to hardware. All the applications that were mining Namecoin drained battery generated excessive heat, or put unnecessary strain on device resources, what is the reason it's now forbidden.
If you want to be a serious Namecoin miner, the first step you should do is join a miner pool. They will help you with your setup and guide you in the beginnings. Then it would be best if you bought, of course, some gpu to get as much value as possible.
It's complicated to say how profitable is Namecoin mining because it varies person from person. It depends on many variables like the cost of electricity, cost of a mining setup, taxes, etc. The best way you can do is to check the Namecoin profitability charts. They will tell you how profitable is Namecoin mining in your location.
A Namecoin miner is just a computer. The main criterium you should look for is efficiency compared to electricity cost. Anyway, it's usually better to buy specialized, professional miners called ASIC. Or you can use gpu, which is the best way how to mine Namecoin.
The best way to start with Namecoin is to start from the beginning - that means mining. This way, you get your hands dirty and get some super relevant experience with this cryptocurrency. For mining Namecoin, we recommend gpu as the best way how to mine.