I recently bought an Android, Samsung galaxy 3 (Marshmallow) on amazon for 73$ to test my current project. (Android, UWP, Win Phone 8.1) It is all set up and working fine now, but I had a major problem with shortcode (text ads) because the phone was advertised as unlocked but was still branded with the att firmware which kept sending cryptic text messages (service is not available) and the firmware would reply. Total of over 200 messages in 10 days,
My problem was the carrier I am using was charging me for those text messages. My solution was to remove the SIM card, and I am still able to tether the device to my desktop and run my app. I have wi-fi and the phone uses it to access the internet, etc. the only thing i can't do is make a phone call, or text on the device.
I am grateful to my mobile carrier "Ting" for giving me credit for all those text messages and not charging me anything. My phone bill for the first month is only 9$. Ting charges 6 for each device and then an extremely reasonable (cheap) pricing structure after that. No contracts So my phone bill for the foreseeable future will be 6 bucks. If I wanted to, i could deactivate the SIM card altogether which would make my phone bill $0. But I am saving the SIM just in case i need it for some reason.
Hope this posts helps someone out there looking for a cheap alternative way to implement testing devices.