Absence - use this activity type for vacation, sick leave, etc.
E-Mail - to keep track of all your inbound/outbound e-mails
External Activity - use this activity type for activity information provided by third-party systems
Fax - to keep track of all your inbound/outbound fax transmissions
Incident - this is the most important activity type in the area of Incident Management; it features many additional attributes and advanced operations supporting the Life Cycle of an Incident - use this activity type to report bugs in a bug tracking system
Mailing - to keep track of all your mailings, letters, etc.
Meeting - use this activity type to plan/schedule meetings, lists of participants, etc.
MMS - to keep track of your picture messages (mobile phone)
Phone Call - to keep track of all your inbound/outbound phone calls, conference calls, etc.
Sales Visit - use this activity type to plan/schedule sales visits, parties to meet, etc.
SMS - to keep track of your short text messages (mobile phone)
Task - to keep track of tasks, things to do, etc.