They own some of the essential patents relating to it. When the standard is being thrashed out, each company declares which of their patents is essential to the standard working. The trick is to get as many of your patents into the standard as possible because then everyone else has to license them from you.
RIM seem to think so anyway. They've just licensed it again...
http://www.nokia.com/press/press-releases/showpressrelease?newsid=1275090
And Qualcomm and InterDigital lost to Nokia over similar, if not the exact, essential to GSM and 3G patent infringements recently. Nokia own thousands of patents relating to GSM/UMTS, many of which are essential to the standard.
I would guess Apple's defence is that they already think they've licensed GSM and 3G patents from InterDigital to the tune of $20 million + royalties or that their off the shelf chipset suppliers have paid up already.
This will just end up with patent cross-licensing with Apple getting a license to Nokia's GSM/UMTS radio technology patents and Nokia getting access to Apple's patents should there be any of merit. Somehow I think Nokia will end up giving up more relevant patents than Apple will though. Apple's patents are usually lame crap like UI gestures rather than actual technology. Apple will look pretty stupid trying to swap finger swipes for UMTS but I guess if that's what stupid people pay money for and Apple has a patent on it, Nokia's only option is to capitulate.