You can put two SIMs in a Dual SIM adapter.
One SIM is active at a time
You can switch between SIMs by going into and out-of flight mode.
Works very good.
You have to get a dual sim adapter that fits in the little room there is between battery and cover.
I use a King of Doublecard, type MAI-E bought on eBay from saintjoy0_3.
The model he advertised was "6220/6310i/7250/8310/T230/T68i DUAL SIM CARD"
(note: looks VERY similar to the one on pdamods!)
Bought it for £6.55 (incl 2.50 shipping)
(note: MUCH cheaper than pdamods)
HTC Vision (Desire Z) with 13th Gen Dual SIM on TMO and Voda
Previously owned MDA Vario IV, MDA Vario and MDA II