I'm using the same ANALOG-Dual-SIM-Adapter from Hot-Wire-Telekom with my Trinity!
You switch between SIM's by using the HTC-Comm-Application (switching Flight-mode ON/OFF)
Procedure: Switch Flight-Mode ON - wait 10-15 seconds - Switch Flight-Mode OFF
Works like a charm, but once in a while I get a SIM-error, but after repeating the switching-procedure everything works fine again. So no problem at all.
Also be aware of the fact that DIGITAL adapters (switch via SIM-Application-Tool) WONT work with UMTS-SIM's!!!!
Took me a long time (and 30 bucks) to realize this.
My Analog-adapter works fine so far with Hutchinson 3G Austria ("THREE" is an UMTS-only Provider) and Telering Austria (GSM-Only Provider).
Well, this is what it is - my theory that I have, that is to say, which is mine and it belongs to me, and I own it and what it is too!
HTC TOUCH HD + 8GB MicroSDHC
Duttys Xtreme ROM v2.4 / Radio 188.8.131.52
HTC P3600 Trinity (black)