Inventory Asset linking question

hi

i am planning on keeping track of my various mobile devices using the asset section of SD+, i often swap simcards from one device to another so i thought about creating a hardware section for the actual device and then another asset entry for the simcard with phone number

is there any way to link these 2 entries? this should not be hardcoded as devices often change but sim card numbers remain the same, the only way i can currently see is to make the actual device (mobile, blackberry) a workstation and associate the sim card asset with this but it would be nicer to link them as assets.

another way would be to create a user for each mobile device and link them that way but that would make it messy, any ideas, does anyone keep track of mobile devices and sim cards seperately? I currently use a spreadsheet

thanks