http://www.zimbra.com/support/support_overview.html
-Support incidents determined to be enhancement requests or bug reports do not count against your allotted support tickets.
-You can exchange as many emails/phone calls as needed to resolve the issue.
I am not a sales person...but it depends upon total subscription amount:
Let's say it was 100 NE Standard w/o Zimbra Mobile, the annual subscription ammount falls under 2,500 so it would fit under the 2-ticket standard support. Adding mobile or 100 of NE Professional (ZCO & iSync are 2 of the biggies
compare ZCS editions) would get you on the 10-ticket advantage support.
More details here:
http://www.zimbra.com/products/pricing.html
Play with
http://www.zimbra.com/quote/configurator.php and you'll see what I mean.
You should contact
sales@zimbra.com or use
http://www.zimbra.com/about/contact_us_form.html for any EDU/Govt/Non-profit pricing as well as anything over 500 accounts as the greater you purchase there's a sliding tier (like any company 5,000 accounts is a lot different than 500,000, etc, etc).