Leads Summary is a way for you to tell whether a lead can be called right away or why it's not able to be dialed. 

In order to get to this, you will need to go to campaigns:

Then go to a campaign's settings and go to the Leads tab.

From here, when you scroll to the bottom of the page, you will see the Leads Summary bar with a Run Leads Summary report.

Click on the calculate button and you should see a summary of your leads on this campaign.

The reason why the leads are not dialable is shown in the summary. It displays why the leads are not able to be dialed by the list not being active, because of the status, "local time" rule, etc.  If you want to make them dialable, you will need to check on your lists to see if they are inactive, in a certain timezone, or if the status is not dialable in this campaign.

• Total leads assigned to this campaign.
• Total leads that won't be called because the list is inactive = Leads are in Inactive Lists.
• Total leads in active lists that won't be called because of their status = Leads Statuses are Not Dialable (check your Dispositions tab. See How to Setup Campaign Workflow Based Dialing)
• Total leads in active lists that won't be called because they are outside of the "Local Time" rule = Leads Local Time is not within the Call Times.
• Total leads in active lists that won't be called due to the Campaigns "GMT Lead filter" = Leads are not in the Selected GMT. See GMT Lead Filter Override
• Total Leads that won't be called because of Campaign's "Drop Lockout Time" settings =
• Total Leads that won't be called because they are part of the DNC database = Phone numbers of the leads have matches in the DNC List
• Total Leads that won't be called because of the "Attempt Second Delay " = Leads won't be added to the hopper until it reaches the Attempt Second Delay. Check the Dispositions Tab. Also, check if the Status belongs to a Workflow Automation that reinserts the leads in the hopper after a certain period of time.
• Total Leads that can be called once you have reset all of your lists = The list reached the Maximum Attempt and needs to be reset.
• Total Leads that can be called now! (note: this is only calculated if agent(s) are logged in to this campaign)

In case of a Ringless Voicemail Campaign, this is how Leads Summary looks like.

Note the inclusion of 'Total Leads that won't be called because their numbers are not wireless' in the reasons.