I'll stop you right there. 3 and Vodafone merged, neither took over the other. In fact I heard that Vodafone was ready to quit the Australian market if the merger didn't go ahead. As it goes now, the two companies are still separate brands and separate networks. I work closely with our business sales representative for Three and he's said that so far it's just been administration that's merged, and the merger of networks isn't even on the horizon.
That being said, you still get free tethering and quasi-visual voicemail. Your 3 voicemail is powered by an email-inbox system and you can set this account up on your iPhone. Voicemail messages are delivered as WAV attachments to emails which you can play back on your iPhone.
Our business operates iPhones and datacards on 3. By our nature we don't leave the metro area of Brisbane, so regional coverage is not an issue. Furthermore, for this reason our financial controller doesn't see the point in paying for a national network (a la NextG) which we have no use for. If we go outside of the metro areas, we cough up 50c/mb during the months we need it rather than paying an extra $20+ every month we don't use it.
I can only talk from the perspective of Brisbane, and haven't got much of an informed opinion of the coverage in other cities. There are only two places where I roam to Telstra's 2G network - the multilevel carpark behind our building which is right next to a distribution station for the rail line which runs behind the carpark, and a deep rail cutting between Park Rd and South Bank station. Everywhere else I have 3 coverage.
My roaming charges last month were $1.81. The month before that it was $0.32. People will scare you with "OMG YOU'LL GET REAMED BY ROAMING CHARGES" and from my experience (and the experience of others in the company) it simply isn't true.
Honestly - I couldn't be happier with 3. I've never had to call customer support (this is a very good thing), my bills have been on time, the expected amount, and $20 for 1GB of data is great value.