1) Welcome to the Party!
2) As you are obviously new here, I have some suggestions to help us all help you:
When you post, please post your entire configuration including (but not limited to) your installation method (7.X.X?) and vicidial version with build (VERSION: 2.X-XXXx ... BUILD: #####-####).
This IS a requirement for posting along with reading the stickies (at the top of each forum) and the manager's manual (available on EFLO.net, both free and paid versions)
You should also post: Asterisk version, telephony hardware (model number is helpful here), cluster information if you have one, and whether any other software is installed in the box. If your installation method is "manual/from scratch" you must post your operating system with version (and the .iso version from which you installed your original operating system) plus a link to the installation instructions you used. If your installation is "Hosted" list the site name of the host.
If this is a "Cloud" or "Virtual" server, please note the technology involved along with the version of that techology (ie: VMware Server Version 2.0.2). If it is not, merely stating the Motherboard model # and CPU would be helpful.
Similar to This:
Vicibox X.X from .iso | Vicidial X.X.X-XXX Build XXXXXX-XXXX | Asterisk X.X.X | Single Server | No Digium/Sangoma Hardware | No Extra Software After Installation | Intel DG35EC | Core2Quad Q6600
3) Features is more of a "Requests for new" board, rather than "is there a way to do this" board. The "How do I ..." board is "Support". Moving your post accordingly.
4) You have two questions, really: First you want to call another number without hanging up this number, essentially a 3-way call to avoid losing the client. This feature is 3-way calling. Use the manual to enable/practice/test. Second you want to allow the agent to modify the existing number OR add a new number to the lead. In campaign modify (detail view) there are options for alternate numbers. The alt_number and address3 fields can each (or both) be used for extra phone numbers for a lead. The agent would add that new number to one of those fields, and then initiate a 3-way call with that number. Then the client would terminate the original call OR the agent could terminate it in the "Show conference call channel information" link. Carefully, of course, to avoid terminating the wrong line.