I would have to guess built in memory. I haven't seen anyone tear one apart yet. I think 1st generation phones were the only models that had the hidden flash card or external slot.
Thanks. I knew there was no expandable memory but wasn't sure about that burried sd card slot like I have on the HTC Surround....it worries me because the Surround is useless as a phone now since it has memory corruptions every Two days. I use it only to goof around with WP7.
i think htc was the only company that uses uSD cards instead of nand for the internal memory on gen1 devices, and all gen2 devices switched to nand for speed and stability.