Is it possible to install and use softphone on Mac using Wine http://www.davidbaumgold.com/tutorials/wine-mac/#part-0 ?
The answer is a definite maybe
It is worth a shot to try it, there are also other emulators available but I am not a Mac guy at all. There are also compatibility issues with Windows 7 and .NET and in a 64-bit environment it is a 50/50 shot, I have read stuff where people have had to install hacked older versions of .NET that are only in Chinese and had to guess all the click though prompts to get it to install... so if you are going to run an emulator make sure it is a Windows XP emulator and not Win7.
Mitel is going more and more to SIP-based applications for everything but Mitel branded phones, so I doubt you will see a true stand-alone softphone by Mitel again unless it is a re-branded SIP phone, like UCX or something.
You should also consider UnifiedCommunicatorExpress, it has a softphone that uses that uses a SIP device license in the 5000, more information and a 10-day free trial can be found at
http://unifiedcommunicatorexpress.com/, again though, it is for the PC and not MAC but it might be more emulator or VM friendly than the 8602.