There is a rumour going around that new docomo handsets will support cookies and send referrers.  Kimura.Memo has an article stating that he has received a request from a docomo user agent using a docomo IP address that sent the headers HTTP_COOKIE and HTTP_REFERER¹.  This means it is potentially an actual handset, however it could also be some sort of test on docomo's part.

In the past, docomo's handsets have not supported cookies.  This has meant for a site to support sessions, a session id parameter had to be added to URLs.  As the other major carriers, au and SoftBank, support cookies, this has caused developers some pain.  However, if docomo's handsets will support cookies, this will make things easier. 

Whether docomo's new handsets will actually support cookies remains to be seen.  If only new handsets support cookies, this will probably change little in the short term, as most docomo handsets will still not support them, and developers will thus need to design for the old handsets as well.  However, it would be a step in the right direction, and mean in the future, developers could start assuming all handsets support cookies, much like they are now doing with XHTML support.

Footnotes

1.  An interesting side note is that referred is misspelled in the header, HTTP_REFERER.