AT&T Wireless Hack: How to use 35Gb of data, without ever pa

//Since I have written this article, new AT&T plans have been release and I have confirmed these methods are still working after I have recently checked my data usage.//
What I am writing to you today about may not last forever. But currently, because of how "Billed in Advance" billing works, AND because AT&T does not currently prorate data usage, there is a way to use much more than your initial monthly data plan allows, for as long as AT&T allows us to make same day price plan changes and for as long as AT&T does not pro-rate data allotments.
I have been testing this out since the mobile share data plans first came out. So for about 2 years now.
There are somethings that you need to be aware; things not to do.
I would not recommend using these methods with plans smaller than 10GB, its simply not worth the efforts.
I strongly recommend not to experiment with this if you are on some type of grandfather'd or retention offer mobile data share plan... (such as a double data plan)... Because if you do, those plans are not available in the self service options to change back to, so you would have to call customer service to get a grandfather'd plan back (that is, if the plan is even accessible by the agent. Best rule here is, if you like your plan; dont mess with your plan LOL).
Now, for those that are curios how this works; lets get started.
Again, this is going to work best *if you are on one of the currently marketed mobile share plans, such as the 10, 15, 20, 30, 40, 50+ Gb options;
Your new billing cycle needs to start out with the highest plan you are willing to pay for.
So if you don't want to pay for more than what the 20Gb plan costs, start with that option.
Do not do any backdating or future dating... All the changes you do, need to be made effective immediately.
So lets assume your billing cycle Just started today! And lets pretend today is the 1st of the month.
You begin your month having full access to the 20Gb plan and 10 days go by and you have now used 19Gb of Data. (Keep in mind here that you have 1gb left over. Its best to have a little left over because I will explain why shortly)
Now, change your plan to the 15Gb mobile share value plan and try to make that last till the end of the cycle. You will have effectively used 35Gb of data, without having had to pay more than what the 20Gb plan cost was. Just make sure on the last day of your cycle, you change back to your 20Gb plan so that you smoothly transition back on to the plan you need for the next cycle.
You will notice on your next invoice that you did not finish using the rest of the days in your billing cycle for the 20Gb plan. So you'll notice a 20 day refund for the 20Gb plan, and charge for the 15Gb that replaces that 20 day time frame. Then as for your normal bill, you'll notice that you begin your month back with your original 20Gb plan as always.
This method can be used MULTIPLE times during the month to allow for even more data usage; such as stepping down from the 30Gb plan, to the 20, then to the 15, then to the 10, and finally back to the 30Gb plan.... Just make sure you always begin the month off with the largest plan you need, and then step it down to a smaller sized option.