@KLiK
Except this is considered stealing... as you are using resources you were not given permission to use. Perhaps explaining to people how they can pick up extremely cheap devices instead would be more appropriate...

Here in the USA, you can pick up brand new dual core phones for as little as $10 USD.

Very bad idea imo. Phones will turn warm and notifications would show up unless you have time to proper config boinc agent. If i were vendor not knowing about boinc, maybe i would wonder if a hacker had installed a bot or something and i would make further steps checking what's going on. Eventually your boinc/project-id would show up and you could maybe get account terminated (if i were tech!)
So you are risking end up fu**ing over yourself.
You want the cheapest 4-core crunching-phones? Then get used kitkat androids with a broken screen for example from ebay or local small ads. Only buy with (original) receipt. The better choice would obvisously be to buy new from the store. At least you're sure battery and charger are of genuine quality. I ordered myself a model called "mlais m52". Cheap 8-cores... but not cheaper than 2 quads. they run on lollipop, crunching is working ok... other parts of OS still need a bit of bug fixing.

Summary: Clients/Shop staff handling them going "Why's this phone warm?"... is it broken? If found out, not an advert for BOINC & WCG!

KLiK, in the weekly ad at a local dollar store (Dollar General) there is a special on the ZTE Whirl 2 and the LG Optimus Fuel phones for $9. Both of those phones are dual core phones. I don't recommend the Optimus Fuel phones as there seems to be quite a few that get swollen batteries quite easily in a very short amount of time but I do have 8-10 of them.

http://www.phonearena.com/phones/LG-Optimus-Fuel_id9333
The Whirl 2 says it has a quad core processor on the box and in the advertisements, but if you do enough searching via Google, you will find multiple posts confirming what I discovered. The phone is actually a dual core phone with the same processor as the Optimus Fuel. Not sure how they haven't been sued over this yet as it is falsely advertising it.
http://www.bestbuy.com/site/net10-zte-whirl-2...728026.p?id=1219362861847

I have also picked up other dual core phones in the past like the Moto e from Walmart for $10 on a special deal. I have picked up some of these phones from Walmart, Family Dollar, Dollar General, and Walgreens so far. I have seen deals on them even at Kroger and its various other chains. The deals are out there if you just look for them. I find that these deals are better than what I typically can find on eBay even when looked at phones with damaged screens. You can also go to places that deal in recycled cell phones like http://c7recycle.com/store/ . They get different phones and price them differently on a weekly basis.

I have ran many phones with BOINC. Yes, some phones have battery issues. Some don't. I find LG devices to be lower quality and find Samsung devices to hold up quite well. YMMV

Edit: And to be clear, these are all pre-paid phones that I never activated. I just hook them to my wifi and let them do their thing.

After recalcing an artificial DCF [since the client is locked to 1.000000, which v6 does not do], now am 39+ days buffered over target, if true. Need 99 more days crunching [5 days], have 138 in theory, even upped the laptop from 1200 to 1800MHz again to speed things up, though 80C is not the best operating temp. When closer will start giving the excess back. Objective to not go over by more than a few hours, like on NRW...

Nutritious Rice for the World 1,934,242 2,287 2:000:13:07:16
or
Discovering Dengue Drugs - Together - Phase 2 1,990,681 4,437 2:000:19:04:14

13 and 19 hours over Sapphire :D