How to find out how many customers actually have contact details
An easy way to find out how many customers you have in SWIM with an email address is to go to the Customer Menu > Find Customers. If you put your cursor into the email address field and type an '@' symbol (all valid email addresses have this in them) and hit 'search'. This will return all customers who have an @ symbol and therefore an email address in SWIM. If you look down the bottom next to the page selectors for your customers you will see the total number next to the number on the current page.
Similarly, if you want to know how many customers you have in SWIM with a mobile number, you can do the same, but put a '0' into the Mobile field and search on that as most mobile numbers begin with a preceding 0.
Alternative methods include exporting your customers as a .CSV to take into Excel and do a column sort on the mobile/email fields to group the customers who have information in those field together, allowing you to delete the remaining customers and get a count in that way.
Another method would be to do a column sort in SWIM on the mobile/email field and then browsing through the pages until you find the point where the list of customers WITH ends and customers WITHOUT starts. You can then take a count using the totals next to the page changers at the bottom of the page.