Hi there, I know this is an old post, buy I just got my dell 5530 wwan card working in Yosemite, if anyone is still interested in using this 3g card (it's all 4g now)
I installed the card in a thinkpad x220 tablet, in network settings 3 things showed up:
Dell Wireless 5530 HSPA mobile
Dell Wireless 5530 HSPA mobile 2
PCI serial adapter
I used the modem script file, in advance modem settings selected "other" and " dell mobile broadband" just like the picture in the first post, then connected any of the two dell wireless 5530 (the pci serial adapter doesn't connect) using my APN as phone number and user/password blank. Works like a charm.
