Can anyone please enlighten me on the standard for the mobile phones used in Taiwan/Taipei (GSM 900 - 1800 - 1900 or… ?)

The main system is GSM 900/1800. At least two of the operators (but possibly all) support GPRS.

There’s also a PCS network (i.e. Japan’s system) which hasn’t got anywhere near the coverage of GSM - I don’t know of anyone who’s got a PCS phone who hasn’t also got a GSM.

3G is still a long way off - Taiwan was one of the last countries to get round to auctioning off the licenses for it (probably a good thing, given the success of everyone else around the world …)

3G installation in Taiwan has started but as most countries worldwide the systems aren’t ready for commercial use yet. Perhaps some will launch by end of this year but to be fully operational, providing a good coverage and quality or services it will take at least another 2 years or more.

That said you best bet is GSM900/1800 - personally I use Taiwan GSM (TaiWan Da Ge Da) but I am not to happy with it.