[Samsung Galaxy Nexus] ChazzMatt:
WHICH RADIO

XXLF1 (Europe, June 2012) was built in the ICS era and came with an ICS OTA update.

All three

XXLH1 (Europe, August 2012) and

UGLH1 (North America, August 2012)

UILH1 (South America, August 2012)

are newer radios than XXLF1 (Europe, June 2012).

Those three are not only the newest radio builds, but UGLH1, XXLH1 and now UILH1 are the only radios to come with Jelly Bean (4.1.x/4.2.x) . All other radios were for ICS (4.0.x) and older.

Radio build date trumps ROM release date. When a radio was built is more important than when it was "released", as ROM releases are often timed for business reasons. The build date of the radio shows how "new" it is, that Google engineers were using the latest research & testing data up to that point in time.

XXLF1 will "work" with Jelly Bean, of course, but a newer build indicates something better -- perhaps stronger connections with weak signals, etc.

So, running 4.2.1 you probably want XXLH1, UGLH1 or now UILH1. What's the difference between the three?

While we can't prove the UGLH1, XXLH1, UILH1 radios were both built at the exact same time, we do know they were built the same month (August 2012) -- which was AFTER Jelly Bean was officially released in July 2012. So, in build date they are all fairly equal.

Google has the "Europe" XX--- radios as the default for the Galaxy Nexus phones, so it's an "international" radio not just a "Europe"-only radio. Yet, then UGLH1 was found in a Jelly Bean OTA update for Canada. "UG" is the designation for North America radios. Therefore, there must be something in UGLH1 optimized for North America in that radio. And now UILH1 was found in a Brazilian Galaxy Nexus JB update. So, something in that radio must be optimized for Brazil an/or South America. (And again UGLH1 and UILH1 were built after Jelly Bean was released, just like XXLH1.)

Choose which one you think works for you. I live in USA and use UGLH1.

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WHICH RIL

Now let's talk RILs...

The current thinking is to flash the RIL for the ROM you are on, not the "radio" you are on. RIL is associated with ROM, not necessarily radio build. THIS IS NEW. Up until now, people have been focused on pairing the same RIL with the radio they are on. Forum member osmosis did the research to prove this new line of thinking. efrant helped in collecting all the data.

So, if you are on 4.2.x, either

XXLH1

and

UGLH1

or

UILH1

radios would be flashed with the RIL for that version ROM you are using.

Thus, if running 4.2.1 (JOP40D), even UGLH1 would be flashed with the

RIL for 4.2 JOP40C (which is also the RIL for JOP40D)

. (See osmosis post below for why.) 4.2.1 JOP40D was a very minor 1MB update for 4.2 JOP40C to correct a couple of bugs. osmosis has confirmed the radio RIL for JOP40C and JOP40D are the same. UGHL1 came from another Jelly Bean ROM release, but if you are using JOP40D you want to use that JOP40D RIL no matter which radio you flash.

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CONCLUSION

Living in the USA and running 4.2.1 Xylon ROM, I'm running UGLH1 (for North America, August 2012) with the "XXLH1" (JOP40C/JOP40D) RIL.

Since you are T-mobile USA on 4.2.1, UGLH1 (North America) radio with the JOP40C/JOP40D RIL would also probably be your best bet. After that, 2nd choice would be the XXLH1 (Europe/International) radio with the JOP40C/JOP40D RIL.

For anyone running any version of Jelly Bean (4.1.x - 4.2.x) those three radios built in the Jelly Bean era are the ones to use. Just be sure to pair them with the RIL for the specific ROM release your ROM is based on.