GAIT:  GSM ANSI Interoperability Team.  A GAIT handset is a handset
that has the capability of using GSM, TDMA (IS-136) and analog AMPS.
The handset is optomized to choose which networks it connects to in a
specific order.  I believe (though am not 100% sure on this) that its
first preference is for GSM networks.  It will then choose TDMA
(IS-136) networks and finally if neither GSM or TDMA IS-136 networks
are available it will chose an analog AMPS network.  In theory anyway
this will give you the best coverage available provided that you can
access GSM, TDMA or AMPS networks.  From what I understand there's no
smooth handoff between GSM or TDMA to the other modes so if you lose
signal your call will drop and your party will have to call you again
or you'll have to call them again.

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There isn't a whole lot to it.  GAIT stands for GSM/ANSI-136
Interoperability Team.  ANSI-136 is a more technical name for the TDMA
standard that is widely used with Cingular and AT&T.  It works much like
a TDMA/AMPS phone, where the phone will try to attain acceptable TDMA
signal before it will attain AMPS signal.

If am not totally correct, please correct me if I am wrong.
GAIT phones, unless set otherwise, will have a GSM home preference, then
TDMA home preference, then AMPS home preference.  After that it will go
to the most preferred GSM roaming partner, then the most preferred TDMA
partner, then the most preferred AMPS roaming partner.  The idea with
GSM being the preferred technology is that the phone, after the TDMA to
GSM transition, the phone will work fine with new GSM system, but still
have TDMA/AMPS as an additional fallback.

==AD

While GAIT will give you the "best possible coverage," actual coverage is
governed by the programming of the SIM, and it won't necessarily give you the
best possible signal in any event.  From prior posts by me:

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Which network the phone will select depends on how the phone is
programmed (on the SIM) by the carrier.  There are four different modes
of GAIT operation:

     * GSM Native Mode: This is where the mobile is homed to a GSM
  network and is operating on a GSM network. In this mode, the mobile
  is able to perform standard GSM type functions including SMS and Data
  services (circuit switched at 9600 or 14400 bps and packet switched
  service if it is offered).

     * ANSI-136 Native Mode: This is where the mobile is homed to an
  ANSI-136 network and is operating on an ANSI-136 network. In this
  mode, the mobile is able to perform standard ANSI-136 functions
  including text messaging using GHOST SMS and Data services (circuit
  switched at 9600 bps).

     * GSM Foreign Mode: This is where the mobile is homed to an
  ANSI-136 network but is operating on a GSM network. At this time, the
  GSM portion of the phone is operational and the network's
  Interworking and Interoperability Function (IIF) handles the call
  delivery and SMS routing from the ANSI-136 network to the serving GSM
  network.

     * ANSI-136 Foreign Mode: This is where a GSM native subscriber is
  accessing an ANSI-136 network. Again, routing of calls and SMS is
  handled by the network's Interworking and Interoperability Function.

In short, a GAIT phone will be "homed" to either GSM or ANSI-136 (TDMA).
Network selection will be based on standard mechanisms in both
technologies.

Suppose that the GAIT phone scans for service and determines that there
are two networks available for selection, an ANSI-136 Neutral system and
a GSM Neutral system. If the PPI (Protocol Priority Indicator) is set to
ANSI-136 Preferred, then the mobile selects the ANSI-136 Neutral system.
Conversely, if the PPI is set to GSM Preferred, then the mobile selects
the GSM Neutral system.

Suppose that the GAIT phone scans for service and determines that there
are two network available for selection, an ANSI-136 Group A (Home)
system and a GSM Group B (Preferred) system.  The mobile selects the
ANSI-136 system even if the signal is better on the GSM system.

Network selection is a function of preferences configured by the
carrier, not signal strength.  It doesn't matter that the signal might
be better on the other technology.

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Selection of network is controlled by GAIT SIM programming by the
carrier.  The phone will be "homed" to either GSM or TDMA (ANSI-136),
and selection of network will be done by standard mechanisms in those
technologies (Home, Preferred, etc.).

* If a GAIT phone finds both a usable GSM Group B (Preferred) network
and a usable TDMA Group A (Home) network, then the phone selects the
TDMA network, regardless of relative signal strengths, and vice versa.
Home takes precedence over Preferred.

* If a GAIT phone finds both a usable GSM network and a usable TDMA
network of the same priority (e.g., Preferred), and the phone is homed
to TDMA, then the phone selects the TDMA network, regardless of relative
signal strengths.  Conversely, if the phone is homed to GSM, then it
selects the GSM network, regardless of relative signal strengths.
------------------------------------------------------------------------

If you are in an area where GSM is not usable and non-Cingular ANSI-136
is usable, whether or not a Cingular GAIT phone would work on ANSI-136
would depend on the type of available ANSI-136 network.  The phone would
select a Partner, Favored, or Neutral network, in descending order, if
there were any such network(s) with usable signal(s).  It would not
select a Forbidden network, except for emergency calls.

So whether or not *any* (GSM-homed or TDMA-homed) Cingular GAIT phone
would work on TDMA in a GSM-only area (e.g., California) would depend on
(1) TDMA roaming agreement(s) by Cingular, and (2) programming by
Cingular to reflect those roaming agreements.  I doubt that anyone here
knows for sure the answers to those questions, and I suspect it might be
hard to get that information from Cingular, leaving us only with
speculation; i.e., we can't say for sure one way or the other.

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 OK, then: how exactly do you tell what mode the phone is in, on a 6340i?
Aaron Worley