AT&T and T/Mobile use a transmission format called Time Division Multiple
Access (TDMA) and their audio is coded using an algorithm called GSM
(General System Mobile).  This is the dominant system outside the U.S.  NLS
digital talking books use Extended Adaptive Multirate Wideband coding, which
is a greatly expanded version of GSM.

Sprint and Verizon use Code Division Multiple Access (CDMA) and a different
speech coding algorithm.  Qualcomm owns many of the patents for this system,
and it is not common outside the U.S.  Some of the prepaid plans, such as
Virgin Mobile, use Sprint's network and technology.

Lloyd Rasmussen, W3IUU, Kensington, Maryland
Home:  http://lras.home.sprynet.com
Work:  http://www.loc.gov/nls
 
> -----Original Message-----
> From: For blind ham radio operators [mailto:[log in to unmask]]
> On Behalf Of Danny Dyer
> Sent: Saturday, September 05, 2009 10:35 AM
> To: [log in to unmask]
> Subject: Re: Blind accessible cell phones
> 
> There's a pretty indescribable by me technical/very different on air
> approach, why those phones are ___Not interchangeable between AT&TOr
> TMobile and Varison, but _Never the two shall meet. dd.