The HTC Desire models are all the same...except the frequencies they use.
If you're shopping for an unlocked HTC Desire, you may be wondering what the differences are between the three models available: the a8181, a8182 and the a8183.
Each of them has the same operating system (Android 2.1 Éclair with HTC Sense™), processor speed, memory etc -- they are identical in every way except for the supported networks.
Even an unlocked HTC phone needs the right wavelengths.
Make the carrier you want to use supports the model Desire you're buying. Example: all three phones will work with T-Mobile, but none will support T-Mobile 3G.
HTC Desire a8181
HSDPA/WCDMA: 900/2100 MHz
Quad-band GSM/GPRS/EDGE: 850/900/1800/1900 MHz
HTC Desire a8182
HSDPA/WCDMA: 850/1900 MHz
Quad-band GSM/GPRS/EDGE: 850/900/1800/1900 MHz
HTC Desire a8183
HSDPA/WCDMA: 850/2100 MHz
Quad-band GSM/GPRS/EDGE: 850/900/1800/1900 MHz
Call your carrier to confirm compatibility.
Nothing is more frustrating than buying technology that isn't compatible with your plans. Call your carrier to make sure the phone will work.
Update: a8182 has a different display type.
bfksc on HTCForums.com clarifies another difference between models:
Another difference is the display type. In the 8182 I have for N/A market is an S-LCD display instead of the Super-AMOLED. Other than that, and branding for Telus, the phone hardware is identical. I should also mention that the Telus branding also disables the EDGE/GPRS data because Telus and Bell do not use it - stupid move since that means all US/CDN travellers going to EU will not have data since the freqs are different for 3G and 2G data is disabled.
However, there is a way around that by unbranding and updating to Froyo 2.2 which will remove the block for EDGE/GPRS and offer more features.