Using GPRS on a train is not very useful for interactive use, but for reading the occasional website or downloading some (not-too-big) files it works well enough (after considerable tweaking).

When I start my link, I always run My traceroute to my ISP's DNS to see how my link is doing in real-time. Which helps to understand what is happening, here is a screenshot of a typical train-ride from Antwerp to Ghent.

This is the output for a mtr -i5 81.169.63.70 and pressing d twice to see detailed latency. The latency build up and slow release happens every time I switch from GSM base station (between 45secs and 3 minutes depending on the stops and the speed).

                                My traceroute  [v0.75]
moria.gent.wieers.com (0.0.0.0)                              Tue Oct 13 20:45:55 2009
Keys:  Help   Display mode   Restart statistics   Order of fields   quit

                             Last  56 pings
 1. 10.61.6.19               ba.......cba.......cba......2.........>?ca1...1.....1.2.
 2. 10.61.24.50              b3.......cb3.....3.cb3................>cba..............
 3. 10.61.97.1               a3......cca2.....1.ca1....3..........3>cba.......1......
 4. 70-63-169-81.infrastruct a2......cba......1cba..2..1..........1>cb3..........?...

Scale:  .:512 ms  1:1130 ms  2:1749 ms  3:3193 ms  a:6907 ms  b:10414 ms  c:16603 ms

Somewhere between Sint-Niklaas and Lokeren.