Pros Phone is built solidly, it's good looking
Full 1080p screen, colors are bright and accurate
Touch screen works very well
Call quality work well, sound is OK, bit fuzzy
Very nice OS, slick, good looking
Camera take decent looking and clear pictures
Cons No flash
No front facing camera
Not a variety of cases to choose from
Summary I have owned flagship phones, prepaid pieces of junk, international phones, flip phones, etc. This Lumia 520 is by far and away the best deal on a phone I've ever seen. That's not to say it's the best phone ever, clearly you can spend hundreds more to make that happen. What this phone did was show that an inexpensive phone needn't be cheap too. As others have said, if you're on the fence, just purchase this already. It's a no brainer. I will note, I did get mine significantly cheaper than the price listed here - the brick and mortar store that makes the OS on this phone was running a demo that knocked off many dollars on any item. Anyway, onto more of the review.
Overall build/design of the phone - The phone is a very basic look which I find better. It's functional and nothing more, but it isn' also abrasive looking or ugly. The back is made of that soft touch plastic and I love that stuff. It provides grip, it doesn't feel 'cheap', and it doesn't scratch/dent easily. All the physical buttons are on the right side of the phone - which is nice too. You can grip your phone in your left hand without pushing some volume button or what not. The buttons are OK to push - the power works best and so does the camera button(which has two stages so you can focus and snap a pic quickly). The volume rocker is harder to push and push quickly, but you can just hold it to turn volume up/down. Also note, if you take the back off to pull the battery or SD card or what not, make sure you put the cover back on very well - mine was off by a tad and the camera button didn't engage. Overall, the phone is built solidly, it's good looking, and everything is laid out well.
Screen - This is always hard as you have to physically look at the screen to decide if you like it or not. I find the panel to be good given the price, size, etc. The resolution is just fine for a 4'' screen. Yes, a full 1080p screen is good, but even as a tech guy I thought it was overkill for a phone. The screen gets bright enough if you set it to high. You can only set it to low, medium, and high. Also you can leave it on auto, which I do. It works well enough and I can always read the screen. Colors are bright and accurate as far as I can tell. You can adjust more specific color things in the settings too. The IPS makes it so you can view it well without having it dead on. I will say it's a very glossy screen so reflections do get noticed. There is some of that dark 'banding' I'll call it at the bottom of the screen. Many phones, laptops, etc. I have, have had this, so I get over it.
The touch screen works very well and while I'm not wearing gloves in the Arizona summer, I did put a cloth over my hand and try it - it worked just as well. No bad touches or anything amiss with the touch screen.
Call quality/data/signal - I'll put these all into the same category as I don't wish to review any specific network. The calls on this phone work well, they sound OK. It's a bit fuzzy, as if you're talking on a cell phone (go figure, but I've had much clearer calls on cell phones recently). Nobody has complained that they can't hear me well. Data on this sucker is HSPA 21, which is fast enough for me. I get the typical 2-5mbps down in my area and about 1.5mpbs up. Things load quickly on the phone, it syncs stuff well, and it doesn't stop my day. My signal strength is about par for my other Samsung, LG, etc. phones, so it's nothing to write home about, but it's acceptable. My old motorola phone still holds a great signal where my other phones struggle, so it could be better.
Software/OS - I won't be reviewing the Windows phone 8 in depth. It's a very nice OS, slick, good looking, gets stuff done without getting in your way. Yes, it has limits. Sure, the available applications are behind iOS and Android, which is a valid concern. The store is also confusing compared to the others, so finding stuff isn't as easy, which is odd given most apps are very easy to use. The included Nokia software is awesome I'll say. Their version of maps and navigation are very good - hasn't failed me yet and just as good as google maps/nav. The Nokia music is great - it beats pandora and google music hands down - simply because it's free. Also, it does work very well. The included software for the camera is nice - nothing mind-blowing but it's useful and I like it. I'll talk about the physical camera more. Mail, messages, phone, etc. are all very easy to use and look nice. Overall, Microsoft did well with the OS here and partnering with Nokia provided a bit of extra 'oomph' to the mix. Go to a phone store and tell the sales people to leave you alone and try out a windows phone for a while to see how it works. That's the only way you'll know regardless of how many reviews you read.
Camera - It's a basic camera. Nokia does well with optics so even though this is 'only' 5mp, it takes decent looking and clear pictures. It doesn't have a flash, which I don't mind anyway - any cell phone with a flash makes pictures look washed out or if you don't use a flash, it's just dark and grainy. It takes pictures quickly and as I said about some of the nice software, you can flash 5 pictures quickly to pick your favorite. I don't get why people slam cameras on phones - they work well enough and aren't the main attraction - some phones come with respectable cameras now but you'll pay for it. If you need that, get one. Otherwise, buy a good stand-alone camera you can use lenses and such on and enjoy excellent pictures.
Overall - I'm impressed with this phone and even more so given the rock-bottom price. It has some signs of a 'cheap' phone such as you must manually pull your SD card out - no spring loaded ejection (this phone can take an SD card, unlike MANY new Android devices and all iPhones. The ability to add a lot more storage, cheaply and quickly, is good regardless.) The screen is a bit glossy, but oh well. It's a full, honest smartphone that has good specs and works scarily well for the price of an impulse buy. Purchase this phone and save yourself money upfront with a cheap phone. Purchase a prepaid plan and save yourself money every month. Don't ever worry about a 2 year contract again!
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I hope this review is help you.