Not even those factory unlocked $500+ high end smartphones like the iPhone 5S itself, Samsungs, Motorolas (or my Nexus 5) can be built to near global compatibility. Yes, definitely dreaming & wishing that you can find something in the sub $100 price range, let alone $50'ish - there is a price tag for multi-band frequencies and for tuning them, let alone optimizing. Devices that are aimed for the Americas do not work or work as well in Asia and/or in Euro .... such take at lot of the GSM frequencies chart that I linked up above - gets even more complicated with 3G, 4G and LTE bands. For years now, we do not have nor use 2100 Mhz, let alone some oversea carriers are now on 2600 Mhz.

The iPhone 5x sold by Verizonwireless, from what I read a while back, seemed to have more bands for overseas coverage vs. the AT&T and T-Mo variant - it's priced hundreds above your budget, for obvious reasons. For business and FT's traveling on business, the employers picked up the tab or costs (owning the devices, of course) but if you are independent or traveling on your own for consulting work, you will have to "invest" in the equipment if you MUST or NEED it to work once wheels down, rolling down the taxiway up to the gate - costs of doing business.

There are services offered on eBay, with money back guarantees, to unlock your iPhone5 once & for all - priced around $70 to $80 - with the code. There are plenty of 1st. and 2nd. generation, unlocked iPhones in service today around the world - so, consider unlocking yours. I've done this in the past with other global devices and it generally worked as advertised, except once for a HTC smartphone as I wasn't on contract long enough with that for them to unlock before I headed abroad again. Eventually, I got 2 identical HTC devices unlocked via VZW for free. Doing this won't affect your grandfathered unlimited data - go to your AT&T users forum to read some of the related discussion and/or google it.

Lastly, short answer to your question about the Motorola K1m is that yes, it will work in 90% + places around the world, including the Americas for voice & text msg, MMS & data browsing are maybe (i.e. compatible bands & data coverage for your "cheap" prepaid local Sim card plans in use) For under $50 USD, not even dinner for 2 at our local diner these days. Dubai Stu's BLU is nice too, dual Sim & similar/better specs, and newer/updated features & larger mSD card capacity, etc. - a steal for $30. @:-)

We can suggest better ones, but it's going to cost you more, quite a bit more - in the $200 to $300'ish range for nearly true all-in-one. Happy online shopping on a Monday morning to you.