We have just released a new plugin for SOBI Pro to add Date field Support in this awesome CCK. While working on a project, we realised that SOBI Pro does not support Date/Calendar fields so we went ahead & made this small plugin which will add this feature.
For those of you who are not aware of SOBI Pro, its a super flexible CCK system for Joomla & can cater to a lot of your requirements.You can get it here.
To use this plugin, download it & install it using the SOBI Pro Applications & it will be available as a new field type when you create a new field.You can download the extension here : 
SOBI Pro Date Field plugin
** Note that we shall be releasing many such small nifty plugins for free. Support for these however will be purely community driven.