Thank you for getting back to us!
Actually all clients who have purchased Sitefinity 3.7 and had a valid subscription on the 14.01.2011 automatically received an upgrade for Sitefinity 4.0 for free. The ones who still have active subscriptions have received all upgrades until now (service packs and the upcoming Q1 release if they have active subscription).
Please feel free to contact our sales team directly with specific question regarding your license and options, we will be happy to assist you further on! You can reach us at firstname.lastname@example.org or on +1.888.365.2779
All the best,
Grisha 'Greg' Karanikolov
the Telerik team