[HD2 Windows Mobile 6.5 Q&A, Help & Troubleshooting] ianl8888:
Yes, that is correct

I'm afraid there is quite a lot of misinformation in this thread - probably the result of incomplete understanding of the Aus carrier systems and perhaps some impatience with learning these, or understanding the simple physics involved

1) Telstra broadcasts UMTS on 2100/850 Mhz

The 2100 Mhz frequency is used in the large cities and big towns because it offers the largest bandwidth for a higher population density, but cannot carry for long distances

The 850 Mhz frequency is used in regional areas because it offers long distances (large areas) of accessibility, but cannot carry many users at once

2) Optus (eg) broadcasts UMTS on 2100/900 Mhz (similar split with these frequencies to Telstra) but its' regional 900 Mhz signal is much weaker than Telstra's (just cheapskating for capital costs and maintenance on smaller population densities that Optus likes to ignore) so the actual area footprint for coverage is considerably smaller than Telstra's

If you like to stay around the cities and large towns (too many carnivorous kangaroos in the bush !!) then 2100Mhz with any of the carriers will do. If you want Internet connection in the bush, then Telstra's 850 Mhz coverage is best. I'm making no comment on comparative costs here

3) EU/Asian countries generally deploy 2100/900 Mhz broadcasts (some carriers use 1900/900 Mhz). As I understand it, the US carriers use 1900/850 Mhz, as do the South American countries as well as Canada and South Africa

From long and hard experience, I KNOW that Telstra's overseas ROAM cover is superior to other Aus carriers although it is limited in access to the UMTS 2100 Mhz frequency - still, this is sufficient in most EU/Asian cities. Outside of these, the older GPRS "E" frequency works OK

4) Telstra's decision to deploy 850 Mhz frequency in the regional areas and not 900 Mhz was based on marketing politics, not on technology

[Accessible GSM frequencies in the HD2 are not limited; it is quad-band for GSM]

5) The Telstra variant of the HD2, and the US variant, can access the 850 Mhz frequency because the hardware frequency filter in the device is tuned for it (this is done on the assembly line - yep, HTC runs different batches according to where the batch is to be sold - the reason is a 2007 US Court-ordered Royalty payable by Qualcomm to Broadcomm for convicted patent infringement on the 850 Mhz frequency)

6) So, how to remove the Telstra marketing straightjacket ROM without losing 850 mhz access ?

FIRST, install HSPL - version 1.

HSPL version 2 does not yet work on the Telstra-branded HD2 as the model ID is not as yet included

THEN, you may install the combination of custom ROM/Radio you choose. I'm using Radio 2.08.50.08_2 + Miri XtraLite version 8 ROM

IF you need to revert to the Telstra initial stock ROM for warranty, just reflash the Telstra ROM from the SD card. You can download this official stock ROM from HTCPedia.com - I suggest that you do this download first, before installing HSPL

Later Edit: Telstra stock ROM also available here - http://xdaforums.com/showthread.php?t=578920

7) IF you want only Optus or Vodaphone, who broadcast UMTS on 2100/900 Mhz frequencies, you are better off buying an HD2 from (say) a UK dealer as the device from there is hardware-filtered for UMTS 2100/900 Mhz. Just make sure you are buying an unlocked device