I have a lumia 710 too. I bought it in the UK over half an hear before I guess and now I am in india. So I downloaded two apps by Nokia recently "Bluetooth sharing" and "ringtone cutter". So I hurriedly opened those apps only to get an error saying "this app isn't supported with the current version of OS but there's an available" so I checked on Zune but it says my phone is up to date.
Here are the details I found on "about phone" :
OS version: 7.10.8773.98
firmware: 1600.3031.8773.12121
So , now I am sure that there's an update available , but I don't get it

PS:
1. I have another lumia 710 (bought together) which still has the stock OS, I tried to update it to 8773 but again zone said PHONE is uptodate. I tried reinstalling Zune but no luck.
2. My phones aren't jailbroke or some thing lime that. I bought it legit, and it still is legit.