As the telephone field isn't a requirement, you could just remove the HTML for it. You'll have to modify a fair amount of files though...
First there is a set where it asks for the telephone number, secondly there is a set where it displays the telephone number given by the user. You can just change the first set, but then you'd always get an empty telephone number option, which might confuse people!
Remove Entry of Telephone Number
/include/client/open.inc.php
(this is where it asks the client to enter the telephone number)
Line 42 remove this:
Telephone:
">
Ext ">
<?=$errors?>
/include/staff/editticket.inc.php
(this allows a staff member to edit a telephone number)
Line 60 - remove this:
Telephone:
">
Ext ">
<?=$errors?>
/include/staff/newticket.inc.php
(this allows a staff member to enter a telephone number)
Line 36 remove this:
Telephone:
">
Ext ">
<?=$errors?>
You should be okay to remove this HTML and it shouldn't affect the layout negatively.
Removing Display of Telephone Number
/include/client/viewticket.inc.php
Line 43 remove:
Phone:
<?=Format:($ticket->getPhoneNumber())?>
Line 77 remove:
Phone:
<?=Format:($ticket->getPhoneNumber())?>
two notes
Removing HTML table rows (the ) from the display portion will rather break your HTML, leaving a bit of a hole in your table - so you're best off replacing the telephone information with some other information, or at least just removing the bits between the and tags.
%phone is used in some email templates, so you might want to remove this to save people getting blank telephone numbers in their email confirmations!
I believe I've covered everything, as ever, no warranty or guarantee implied
Good luck
