[AT&T, Rogers, Bell, Telus Samsung Galaxy S III] smelenchuk:
Hi all! After spending some time helping others get mobile data connections on their i747 and i747m up and running again, I've come to the conlclusion that a lot of hassle could be saved if a lot of the problems and solutions I and others have encountered and used were compiled in one place for easy reference.

I intend to come back and update this thread as more problems / solutions become available; feel free to post here if there's something I've missed that should be listed here.

To avoid confusion in terminology between stock and AOSP ROMs, I'm going to refer to network types by the name of the technology that powers them and not 3G/4G labels. For a quick reference, EDGE normally corresponds to 2G, UMTS normally corresponds to 3G, HSPA/HSPA+ show as 4G on stock and H/H+ on AOSP-ish roms, and LTE shows as 4G LTE on stock and 4G on AOSP-ish ROMs.

So, find the section below that most matches the problem you're seeing, and see what we can do to help!

----

Table of contents

1. General pointers / I'm not getting any data at all!

2. I'm only getting an EDGE signal / data.

3. I can get UMTS data, but not HSPA / HSPA+ data.

4. I can get HSPA / HSPA+ data, but not LTE data.

5. Carrier-specific issues

----

1. General pointers / I'm not getting any data at all!

Before you get started trying to connect to specific types of data networks, make sure that your SIM card and mobile data plan support the type of network you're trying to connect to (this is mostly a problem with LTE these days, but if you have a very old SIM card you might also run into problems with HSPA/HSPA+).

Keep in mind that your telco probably doesn't have all of its networks available in any given location; if you can't connect to a particular network in a given location, there's a good chance that you just don't have network coverage for that type of network in that area.

Also remember to check if the mobile data toggle on your phone is on (Settings -> More... -> Mobile networks), and that it's set to connect to the appropriate network types (e.g. that you don't have a "Connect to 2G networks only" toggle on when you want to use something other than EDGE). In particular, those on AOSP ROMs (I have not double checked if this is doable on stock) can dial *#*#4636#*#* to enter a settings menu, go into "Phone information" from that menu, and scroll down to a setting entitled "Set preferred network type" which shows what types of networks the phone baseband is currently configured to connect to. This setting has a tendency to be reset while flashing a new ROM, so it's not a bad idea to check the setting on a regular basis.

If you've done that and you're still not able to connect to your desired mobile network type, the next step is to check your device's Access Point Name (APN) settings, under Settings -> More... -> Mobile networks -> Access point names. You should obviously have an APN related to your current service provider active. Although most stock images and ROMs should have these filled in properly already, it's a good idea to check them against a known good set of settings; as a point of reference, you can find a list of LTE APN settings over in this thread.

Lastly, one step that several people have reported success with is to reflash your modem baseband firmware. The images are available in this thread, and are flashable with most non-stock recovery images.

----

2. I'm only getting an EDGE signal / data.

This is most commonly caused by your phone losing its IMEI, which can occur sporadically when flashing new ROMs. This thread contains information about and a tool for restoring your IMEI to your phone.

----

3. I can get UMTS data, but not HSPA / HSPA+ data.

Outside of the problems listed in 1. above, this mostly seems to occur in Android 4.2-based images. Android 4.2 is designed to "ramp up" to HSPA/HSPA+ data only if the phone is actively using data; that is, if you're not actively using data (in a non-LTE area), your phone will default to a UMTS connection - this is to save battery life. Thus, chances are you can get a HSPA / HSPA+ data connection, and your phone will just not do so until it needs to do so.

----

4. I can get HSPA / HSPA+ data, but not LTE data.

Most of the issues that cause this scenario are covered in 1. above - lack of LTE coverage, not having an LTE SIM, not having an LTE APN set, and/or not having a correct network type set are the major ones. Beyond that, you may want to refer to some of the LTE-specific threads in these forums for additional insights, such as this thread.

----

5. Carrier-specific issues

Bell: You may need to have "national data roaming" enabled for your device to connect to the Bell network.

Rogers: Several ROMs have been known to get the Rogers LTE APN data incorrect. As reproduced from other recent threads, here's what I believe to be a known good set of settings:

APN: ltemobile.apn

Proxy: <not set>

Port: <not set>

Username: <not set>

Passwors: <not set>

Server: <not set>

MMSC: http://mms.gprs.rogers.com

MMS Proxy: 10.128.1.69

MMS Port: 80

MCC: 302

MNC: 720

Authentication type: <not set>

APN type: either "*" or "internet + mms" (reports vary)

There have been reports that the old APN settings may need to be deleted entirely for this to stick.

----

I hope this helps some of you out, and saves you some time and effort in getting things up and running again. :)

If you're encountering issues that I haven't addressed here, and/or have solutions to add that I haven't thought of yet, please be sure to come by this thread and make a note of it here.

Good luck!