from http://iphoneforest.com/apple-posts-job-openings-for-3g-iphone-testers.html
Apple Posts Job Openings For 3G iPhone Testers

Apple has posted some interesting Job listings on several of their
international websites that appear to be related with testing the 3G
iPhone. One listing for a position based in Sydney, Australia, asks
for someone who has “technical understanding and experience with GSM/
GPRS, EDGE, CDMA and UMTS”. The person in that position will be in
charge with investigating connectivity issues reported by customers
and field operatives.

      What’s confusing about this is that GPRS, EDGE, and GSM are
already used in the iPhone, but CDMA is a different technology
altogether.

       The description makes mention of “testing and debug of GSM
communications systems” and “experience in field testing and knowledge
of interworking of cellular carriers”.

       More listings based in the UK are for the positions of iPhone
Field Validation Engineers, listing identical credentials. A position
in Germany is open for an iPhone Certification Project Manager, who
“will apply his/her detailed technical knowledge of wireless standards
(3G, Wi-Fi) to understand, prioritize and resolve issues found during
certification”.

...

Could it be that CDMA causes interference with some GSM phones?