Gary,

There are some upcoming announcements about RTC support on the mainframe
coming up in the next few days in preparation for RSDC (Rational Software
Developers Conference) which runs next week. Watch this space.
There is a heads up on the following page as well:

http://www.ibm.com/developerworks/spaces/jazz?S_TACT=105AGX01&S_CMP=LP

Excerpt:
Jazz-based Futures will be demoed at RSDC "Rational Labs." Check out demos
of
Jazz REST Services
Enterprise Reporting / Vega
IBM Rational ClearQuest hosted on the Jazz Platform
IBM Rational Team Concert for System z (Wow!) and System i
IBM Rational Quality Management and Requirements Definition Solutions
Visual Studio .Net Integration with Rational Team Concert

You can see the full agenda for RSDC at:
https://1bosweb3.experient-inc.com/Events/Rational/RSDC2008/Agenda/agenda_search.cfm

You'll notice some other venues in the above list besides the Rational
Labs that talk about RTC on system z and i.

Excerpt:

EM10 Collaborative Software Delivery Using IBM Rational Team Concert for
IBM(R) System z(TM) and IBM(R) System i(TM)
Wednesday, June 4, 10:00 am - 11:00 am
Sean Babineau, System i Application Development Tools Architect, IBM
Rational software
Alex Akilov, Chief Programmer - Rational Team Concert for System z/i, IBM
Rational software

IBM Rational Team Concert (RTC) for IBM(R) System z(TM) and IBM(R) System
i(TM) are new offerings that provide an integrated set of collaborative
software delivery lifecycle tools, including source control, change
management, and build and process management. These offerings target the
specific needs of IBM System z and IBM System i software practitioners,
including specialized support for traditional language artifacts such as
COBOL and RPG, as well as practitioners engaged in multi-tier software
development or application modernization efforts.

They're here! The beta versions of RTC with the Jazz team server running
on the z/OS and IBM i platforms can now be downloaded from Jazz.net. Note
that this first beta drop is simply a repackaging of the base RTC 1.0
product so that the server can be installed and hosted on the IBM i and
z/OS operating systems. That is, no new features are available yet for
supporting development tasks specific to those platforms (e.g. COBOL or
RPG development). However, if you want to try out hosting the Jazz team
server on these platforms, you're welcome to try them out and send us
feedback and your suggestions for improvement.

Check out the Betas download page:
https://jazz.net/downloads/rational-team-concert/betas

Fantastic news I've already distributed the link to other colleagues.