Why Samsung Galaxy S III always stuck with the Edge network
After bit of research I have found the solution to the problem.
The information about this is very hard to find. So I have compiled useful information into this post. I am sorry guys I have given basic instructions only and I guess you are comfortable with these terms. And it is very late and I am writing this so that other can save time doing researching this stuff.
First of all the issues is to do with the carrier and the handset's operational frequency.
Use following links to get more information about T-Mobile frequency ranges ( I can't post any links in the reply
Checkout T-Mobile site for frequency ranges.
My phone spec is as follows;
Model: GT - I9305
Android Version: 4.1.2
Kernel Version: 3.0.31-1153417
For Samsung Galaxy S III;
To get what frequency the phone is currently using type the service code; *#0011#
My Samsung Galaxy S III uses; PCS 1900
This means my phone currently uses UMTS 1900 frequency range.
Now the cool part is you can access your Samsung phone's hidden frequency settings by service code; *#1973286403#
But the result screen is different in each Samsung model.
My screen shows following. It is not the same for all Samsung models. So you have to play around a bit with those menus.
[run EFS SYNC()]
Go to UMTS > DEBUG SCREEN > PHONE CONTROL > NETWORK CONTROL > BAND SELECTION
Under that section by default the value "Automatic(*)" has to be selected.
If you need to check what WCDMA frequency band phone is using navigate to
UMTS > DEBUG SCREEN > PHONE CONTROL > NETWORK CONTROL > BAND SELECTION > WCDMA Band Preference
Under that section you can select what frequency to use if you know your carrier frequency.
But in my case the phone supports 850 MHz, 900MHz, 1800MHZ, 1900MHz, and IMT 2000 (which I think 3G)
Unfortunately T-mobile uses 1700MHz and 2100MHz band for their 4G HSPA+ network which will not fall into my phone's supported frequencies.
So this is the reason behind your phone not picking up the 3G or 4G signals (in T-Mobile’s case 3G will show up as 4G).
To resolve this you can install a custom rom with modified antenna frequency. But I would warn about that because that could seriously damage you antenna and drain battery etc..
I have some more information on this but I will keep them post as I get time.
Please note I am software developer myself not a network engineer. So I would appreciate if anyone with enough experience to add more comments on the network aspect of this issue.