I emailed mobile-l and wikitech-l about this, now I'm moving this discussion to wikimedia-l. Here's the longer technical thread:
http://lists.wikimedia.org/pipermail/mobile-l/2014-April/006884.html
In summary, to show Wikipedia Zero banners for the correct mobile networks, we are planning once for each cellular-based app session to log two pieces of data in a specialized logfile, deleting log entries older than 90 days.
1. MCC-MNC http://en.wikipedia.org/wiki/Mobile_country_code code (format is ###-##), which denotes the mobile operator 2. Exit (gateway/proxy) IP address * These data points would not be logged alongside the normal web access logs.
This information could be used to estimate rough demand for Wikipedia in potential Wikipedia Zero geos, although remediating the out-of-sync IP addresses on file for existing partners is primary.
Internal review suggests this is in alignment with privacy policy, and we wanted to see if there were other thoughts on this approach here on wikimedia-l.
-Adam