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When running a fresh ROM, the APN settings are defined by the SIM card inserted, downloaded from the network via some handshake protocol or are they predefined in the rom for each network ?

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2 Answers

up vote 6 down vote accepted

They are included in Android. The correct settings are determined by your SIM MCC and MNC (Mobile Country Code and Mobile Network Code). If you want, you can view the list of preset APNs by looking at the source code, for example at android-source-browsing.

The file name in this case is /etc/apns-full-conf.xml, but apparently it varies.

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On my latest "upgrade" (a new device), I've got 3 "Service SMS" from my provider immediately when the device was turned on. Do those have any effect, or is it really restricted to what's in the sources? –  Izzy Apr 18 '13 at 11:20
    
Some carriers send the configuration settings when they detect a new IMEI or ICCID+IMEI combination, but usually these are the same settings that come with the device. If the carrier is uncommon, then the settings that come from your carrier may be more up to date. I suggest trial and error. –  onik Apr 18 '13 at 11:30
    
settings that come from your carrier may be more up to date Yepp, that's clear. My question was rather if they have any "effect" (i.e. are applied to Android settings), as one hears different things toward that. Support often says they don't do -- but others report they do. I was not able to check back then, as the content was not displayed, and I had not looked up the "previous settings". –  Izzy Apr 18 '13 at 11:36
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IIRC, on vanilla Android they work. But on carrier/user/manufacturer modded ROMs mostly not. I had to install them once on a CM7 device, but otherwise I've had no use for them. –  onik Apr 18 '13 at 11:44
    
Thank you, onik! Maybe you want to edit that into your question directly, as I find this an important point. If you can find a source for that, all the better. Meanwhile +1 from me :) –  Izzy Apr 18 '13 at 11:46
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Next to the pre-configured settings from /etc/apns-full-conf.xml as described in onik's answer, some providers offer to send you so-called "service SMS" for an automated configuration. Opinions on those are quite confusing: Some say those do not work on Android or iOS devices, and you'd have to enter APN data manually (e.g. Simyo in Germany), while others even let you select your device in advance to send you a tailored service SMS (e.g. T-Mobile Gernamy, where I selected an SGS3 and then was asked to enter my phone number to receive the SMS; or Base Germany, which is the same provider/network as Simyo; one might say that's due to the fact that Simyo is a discounter brand).

I'm with mentioned provider named Base (belonging to the E-Plus group). When I got my new Optimus 4X, inserted the SIM, and started it, I immediately got 3 Service-SMS, which were "executed" on my device. I unfortunately did not check the configuration before, so I cannot say what effect they had (if any) -- but at least I've got no error messages, and everything was working fine.

Edit: Comments from onik (on his answer) and Compro01 (here, see below) indicate: whether those "service SMS" do work or not, might well depend on the (device and) ROM used.

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On all Android devices I've tried it on, on my provider (Sasktel), I get an SMS shortly after inserting the card that my device cannot be automatically configured with a url to go to to get the proper APN settings. –  Compro01 Apr 18 '13 at 14:18
    
Thanks for the hint, Compro. I included a note with my answer. I never got the SMS you mentioned; instead I've got those "service SMS" two times on a new device (LG Optimus 4X and Samsung Galaxy Ace 2, both stock-ROM), where they were processed without any error message. –  Izzy Apr 18 '13 at 14:40
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