From http://3g4g.blogspot.com/2010/03/ipv6-transition-in-cellular-networks.html

IPv6 is good and we all know that. I has been talked for years but practically it hasnt found much success. Verizon
made some noise last year but I am not sure of the conclusion.

Just to recap, IPv4 was introduced back in 1982 and IPv6 work started since
1995. IPV4 uses 32 bit (4 bytes) addresses while IPV6 uses 128 bit (16
bytes) addresses. Theoretically we would now have 2^96 times more
addresses than in case of IPv4.

Most of network infrastructure manufacturers have their equipment ready for IPv6 as some of the handset
manufacturers. The main driver being that someday soon IPv4 addresses
would be exhausted (Internet Assigned Numbers Authority will run out of
IPv4 addresses in September of 2011, based on current projections) and
their equipment would be ready to provide IPv6 addresses without any
problems.

Recently, IETF-3GPP Workshop on IPv6 in cellular networks was held in San Francisco, USA on 1 - 2 March, 2010. There are
lots of interesting presentations available here
for people who want to dig a bit deeper. The concluding report that
summarises the presentations and discussions are available here.
Here is a brief summary from one of the reports (with links at the
end):

Summary

• Scenarios for IPv6 migration were discussed based on 3GPP Technical Report 23.975
• • The discussion focused on validating the scenarios
• General IPv6 transition and deployment guidelines were outlined based on input from IETF
• Solutions for migration and v4-v6 co-existence were presented
  
• • Solutions included existing RFCs and working group items but also proposals in Internet Drafts
  • Gap analysis wrt transition scenarios was discussed

Conclusions on scenarios

• Scenarios 1 and 3 based on dual-stack and IPv6-only deployments were generally recognized as valid
• • See docs IPW100013, IPW100028
• Scenario 2 was also recognized as valid, addressing two separate problems related to insufficient RFC1918 space and subscriber identification
• • See doc IPW100027
• Scenario 4 did not receive wide support from the workshop, largely because it was felt that it addressed a problem already solved by other scenarios
• Variants of some of these scenarios were brought up during the discussions, conclusions were not reached on these
• • These may need further discussion

Conclusions on solutions

• It was recognized that necessary support in the network and devices is already available to “switch on” IPv6 in 3GPP networks
• • Some networks reported running dual stack
  • Some networks reported running IPv6-only now
• Solutions enhancing existing mechanisms for dual stack deployments and new solutions for IPv6-only deployments drew wide support
• • Gateway-initiated Dual Stack Lite
  • Stateful IPv4/IPv6 translation

Next steps: 3GPP

• IETF and 3GPP are expected to focus further work based on the conclusions of the workshop
• • Note that the workshop itself does not have the mandate to make formal decisions
• 3GPP is expected to identify possible normative specification impacts, if any, of the preferred solutions
• A need was identified to provide more operational guidelines about IPv6 deployment to 3GPP operators
• • The best location for these guidelines is FFS (e.g. 3GPP TR 23.975, GSMA, etc)

Next steps: IETF

• IETF and 3GPP are expected to focus further work based on the conclusions of the workshop
• • Note that the workshop itself does not have the mandate to make formal decisions
• IETF is encouraged to continue working on stateless and stateful IPv4/IPv6 translation mechanisms
• • These mechanisms are being worked on in IETF BEHAVE group
• IETF is also encouraged to consider new solutions that are not yet working group items
• • Gateway Initiated DS Lite
  • Per-interface NAT44 bindings addressing IPv4 address shortage
• Note that the workshop has not set any timelines

Further reading:

• 3GPP TR 23.975: IPv6 Migration Guidelines, Release 10 (http://www.3gpp.org/ftp/Specs/archive/23_series/23.975/)
• 'IETF-3GPP Workshop on IPv6 in cellular networks' Workshop Presentations (http://www.3gpp.org/ftp/workshop/2010-03-01_IPv4-to-IPv6_with-IETF/...)
• 'IETF-3GPP Workshop on IPv6 in cellular networks' Workshop Summary Report(http://www.3gpp.org/ftp/workshop/2010-03-01_IPv4-to-IPv6_with-IETF/...)
• 3G Americas Report on 'Transitioning to IPv6' (http://3gamericas.org/documents/2008_IPv6_transition_3GA_Mar2008.pdf)
• Is IPv6 Finally on the Verge? - Light Reading (http://www.lightreading.com/document.asp?doc_id=189143)
• Jari Arkko's Publications (http://www.arkko.com/publications.html)