Hi, I had this problem of the light blinking out when I was trying to put in bank passwords, etc.  I found that if you lay the phone down FLAT, on a flat surface, not in your hand, not half way up to your face, etc....but LAY IT DOWN FLAT, preferably on a hard surface, like a desk or book or something,  the light seems to stay on so that you can enter your passwords for your bank account.

In addition, in case you are also having THIS problem, I  discovered early on that you have to MUTE the numerical keypad COMPLETELY in order to put in bank passwords, etc. or they won't take.    The phone will dial a regular ten digit number, but once that happens, and you try to dial the bank checking account password for example, when the phone is anything but on complete MUTE KEY PAD, the microphone reverberates to the point that it doubles your password in a echo fashion and the bank won't take it.   Example, your password is  1234 ....if you don't have the micraphone on MUTE, the password will be reverbed  as  11  22  33  44     and then, of course, your bank won't take it.  I saw this solution on another android forum.

All I wanted was a smart phone that worked.....I didn't want to move heaven and earth to figure out how to practically rebuild this darn thing to get it to work.