I recently installed onavo for iPhone. My idea was that shrinking the data not only saves money, but also waiting times. Also the report about what consumes data and how much is handy.

After the installation I started the program and a simple wizard helped me change the settings (accept and that’s it) and I was on my way. The first time my e-mail app used the new profile it reported an untrusted certificate, but accepting it solved that.
Onavo reports about 22.34Mb saved in a week. The next week was 40.8Mb. I’m waiting for my bill to see no surprices are on there.
I didn’t notice any speed improvements. Maybe there is nothing to improve as I’m using 3G. Sometimes the connection falls back to GPRS but that is slow as always.
Only downside would be that all my trafic is routed through onavo’s service. Will they play nice with this information?