CRM 2011 SMS custom activity Characters Remaining field
Paul Nieuwelaar in his blog has implemented some javascript for the characters remaining field. This saves me a lot of time from reinventing the wheel. All I then did was to set the default value to the field (160 characters for SMS). Also make sure that you put the 160 limit on the multiline textbox, but leave the minimum value for the charactersremaining field to be -20000000 to avoid the annoying message box. Hope this helps, Andreas