Well - had the same problem with Call of Duty 3 while playing on 3G. You should try opening up an unrestricted APN, it did the trick for me. Just go onto Vodacom's website, fill in the disclaimer form, email it back to them and you'll be able to use the unrestricted APN for gaming. Beware though, it opens up all incoming ports as well, so I wouldn't use it for normal internet browsing. Luckily you can switch between APNs for different circumstances...
Good luck!