Calypso/Iota/Rita chip recommendations

historical

Hello fellow Calypso phone hackers,

Not having found an already-existing Calypso phone that is exactly to
my liking (of the ones supported by OsmocomBB, the Pirelli comes
closest to my ideal, but even that one has a few things I don't like,
and most important of all, the availability of these phones on the
market has already shrunk down to zilch - so the day is near when it
will be just as legendary-unobtainium as the TSM30), I am setting out
to build my own.

I am setting out to design and build a new Calypso/Iota/Rita phone,
one that will be specifically designed to run Free Software as its
firmware: either OsmocomBB or FreeCalypso (my own personal alternative
free GSM firmware implementation), up to each user's individual choice.
My design will be a phone, not a modem (i.e., complete with the
essential UI elements, as in LCD and keypad), and it will be a
dumb/plain/feature phone, i.e., the Calypso will be the main/sole CPU -
not a smartphone like Openmoko etc.

Before I tackle the difficult problem of either making a new plastic
case or choosing some existing one, I will start out by building a
bare GSM development board - basically a complete phone sans case,
built on a non-form-factor-controlled PCB.  This development board
will probably end up being very similar to the one which Harard Welte
has announced here a little over a year ago, but with one major
difference: *all* hardware design source files (as in schematic, BOM
and PCB layout source) will be openly released, with absolutely nothing
withheld, and in fact the development itself will take place in a
public source control repository.  Therefore, regardless of whether I
succeed or fail in the ultimate goal of producing a complete phone
packaged in a plastic case, there will be an Open Source Hardware
design for a working Calypso GSM board which others will be able to
use as a starting point - something that wouldn't be possible (or at
least less convenient) with Harald's PDF-schematics-only version.

However, the above vaporware announcement is not the real purpose of
my post.  Instead, I am currently in the negotiations with several
Chinese sellers of Calypso/Iota/Rita/etc chips, and I'm soliciting
advice on exactly which variant of each chip I should use:

* The Calypso chip in both GTA02 and Pirelli DP-L10 (the two existing
  designs I use as references to be copied whenever it makes sense) is
  PD751992AZHH.  I can easily get this exact part, but I can also get
  ones with GHH or AGHH suffixes.  I'm venturing a guess in that the A
  seems to go with the 751992 number, i.e., it's part of the die
  revision, and as to the difference between GHH and ZHH, I'm guessing
  that it's the RoHS difference: I'm guessing that GHH has balls made
  of real SnPb solder, whereas ZHH has the "lead-free solder" junk
  substituted instead.  Because I'm very fortunate to NOT live in the
  EU or anywhere near, I'm not subject to any EU-nian laws like the
  RoHS idiocy, and I generally prefer to use real SnPb solder whenever
  possible.  So I wonder: can someone confirm if indeed PD751992AGHH
  is the exact same Calypso chip as the PD751992AZHH used in the GTA02
  and Pirelli phones, but with real non-RoHS solder balls instead, or
  is it something different?

* Which Iota variant is better: TWL3014 or TWL3025?  I'm thinking
  TWL3025, reasoning that it being newer probably means having some
  internal bugfixes or minor improvements, but perhaps the older
  TWL3014 is better instead?

* As to the Rita, the base part number appears to be TRF6151C in all
  phones currently supported by OsmocomBB, so I'm sticking with this
  base part number.  But there are additional suffixes after the 'C'
  in that P/N - would anyone happen to know what these suffixes mean,
  and which variant I should use?

* For the RF PA, I see that the GTA02 uses RF3166 from RF Micro
  Devices (one of Harald Welte's posts regarding his planned Calypso
  board also mentioned him planning to use the same PA), whereas the
  Pirelli and most other feature phones supported by OsmocomBB tend to
  use Skyworks parts instead.  Which is better?  I'm currently leaning
  toward the RF3166, but if someone has a recommendation that is
  actually backed by some knowledge/reason rather than just a guess
  like mine, I'll listen. :-)

* If I do go with the RF3166, any idea as to what the different suffix
  versions are?

TIA for any input,
SF