Hi,
A few options for you (you don't say if you're using crm v4.0 or 2011 so I'll give options for both)
V4.0
- Create your phone call activity via an on-demand workflow that includes dynamic insertions of the extra phone number fields. For added ease, add a button on your lead form that fires this workflow.
- Add jscript to the phone call form that fetches data on load from the lead (if regarding = lead) and populates the extra fields. Also fire the script on change of the the 'regarding' field to cater for the regarding lead being changed.
2011
3. In addition to above, you could add an html web resource in conjunction with a jscript web resource to display the extra phone number fields.
Hope that gives you a direction to persue,
Rob
Microsoft Certified Technology Specialist (CRM) GAP Consulting Ltd.