I have had a consistent track record of data use over many years and several phones. My current wifi plan is for double the amount of data I typically use.
In mid-December (2013) it jumped dramatically. About the same time I noticed that I was seeing a "your wifi is unstable" notice, but I didn't think too much of it at the time. About 3 weeks into January's billing cycle I got a notice that I had use 75% of my data. I have not ever seen this notice before, so you can imagine it got my attention. After doing a lot of reading here and other sites, I found that in fact my phone was not connecting to wifi anywhere.
After 5 hours of Live Chat, emails, twitter, and finally a phone call on a wasted Saturday - it was determined that my phone was now defective. Something to do with the last system upgrade changed the battery management, which caused too much heat, which led to something physically breaking in the wifi of my phone. I was told it is hopeless and there is no fix, only replacement. Because (and they were very clear *only* because) it was still under warranty they sent out a new phone. They promised it a) would not have this issue and b) it was fixed to not develop this issue in the future.
Got the replacement phone in yesterday. It would not connect to home wifi. I decided to take it to work today where it does connect. Came home, still doesn't connect at home. No equipment has changed in the last 6 months. The Actiontec router works fine with every other wifi connection and there have been no changes to the router settings since original install.
I run a small business and need to be able to do so from home, and in the field. If I can't get this fixed, and soon, I am going to have to move to a different phone, with a different carrier ETF or not.
I welcome all possibilities.