I want to configure task object under Activity. I need to add a field mobile in to task object. I need to show the field on the task page and on the reminder window. For this I try to create a new field on task object but not able to find the any option to create a custom field on task. Please help me to resolve this issue. My salesforce account is a group Edition.
For custom task and event fields, click Your Name | Setup | Customize | Activities | Activity Custom Fields.
There are certain limitations though, for eg you can't create Lookup fields, but you should be alright for Mobile.
It is however not currently possible to customise the activity reminder popup, so you wouldn't be able to add Mobile on there. (Some people append it to Subject if they need to see it on the reminder.) http://success.salesforce.com/ideaView?id=08730000000HB98AAG
Even though you can have custom fields .still you cannot have on pagelayouts .
Please see the idea
Its running under ideas .Please do vote for this.