The only thing I’ve noticed so far is that the offline mode doesn’t seem to be really offline with this thing in, because my battery now runs down a lot faster in offline mode than it used to. It’s no biggie, I’ll just switch the phone off or take out the twin SIM on flights, but it’s something to watch out for. It may just be a peculiarity of my setup, of course.
The other thing that’s not really clear from the site is the compatibility of handsets. The site has a long list of compatible handsets on it, which includes a lot of standard 3G and other phones, but even though the Nokia 6110 Navigator I upgraded wasn’t on the list, it still worked fine. So maybe it’s a matter of taking a gamble if your handset is not listed? Oh and remember you’ll need a phone with a back cover which bends enough, or has enough room to cope with the extra SIM.