by Chris » Wed Jul 14, 2010 10:14 am
It would be very difficult if not impossible to give you a reliable answer to this question because everyone's data usage is different. For example, I use very little data for the voicemail fetch because I rarely have more than one voicemail in my account while other users may keep all of theirs. SMS varies much more because a given user may have many more messages per conversation (we fetch 10 conversations rather than a limited number of messages).
I would recommend setting the SMS Auto-Refresh setting to Disabled, Slowest, or Slow and monitoring your data usage throughout the first few months. Also, having a large number of contacts (especially with photos) that change frequently will eat away at your data usage. Now that iPhone users have metered data plans, maybe we should consider an option to disable contact photos.