we have telephone numbers "normalized" using E.164 notation, e. g. +49123456789,
used in central address books etc.
The e.164 standard includes support for the + sign that is typically used in International dial plans,
but not very often in North American Numbering Plans (NANP) implementations.
Cisco IP Phones like 7906 are able to cope with those DNs starting with the "+"-sign (appropriate
route are present)
Unfortunately Cisco IP Communicator ("Soft phone") and also 7921 (wireless phone)
are ignoring the leading plus sign when using numbers e.g. in call history lists
(numbers starting with the + sign by holding down the 0 key being typed in are
CUCM 7.1.2 is used - is this issue fixed with later CUCM versions?
The CIPC defect that addresses e164 support can be found here:
Unfortunately it is not yet resolved
For the 7921 I couldn't find anything off the top of my head.