That one is hard. So many moving parts, and a lot of sales volume.
The things I can think of to consider are:
profit margin (separate category, always important, but predicting it
The plus side of the analysis is that there is a lot written about
each company and the industry. Short of reading that, Elle's comment
is very practical. It's clear that cell-phones are not going away, and
are expanding capabilities. When in doubt, watch the bottom line.