Currently in Japan where I'm using the CelTrek SIM in preference to other options (I have only one WCDMA-2100 phone). While it seems to roam only on Vodafone-JP (a.k.a. J-Phone, SoftBank) the coverage is pretty good. Incoming calls are 24c/min, which gets pretty close to the about 19c/min to forward calls from the US to Iceland to use my 09 SIM and outgoing calls to the US are 34c/min. I took a brief call a couple of days ago and was charged only 12c. So, the billing is on some granularity less than one minute.
Their webpage allows me to download voicemail as an audio file and has very detailed call information. I haven't had much need to make a lot of calls since my room here has high-speed network access and I can make VOIP calls to the US for 2c/min.
I just keep thinking about those days when to make an international call when traveling, you had to go to the local telephone office, be assigned a phone booth, then return to the counter and pay. In many countries you couldn't make international calls from a regular public phone. Now we tote little phones on our belts that work just about anywhere and cost much less to use per minute than thoes calls I made in the 70s and 80s.