using a standard mini- to full-size cable plugged either in to the 3G socket,
I just had a look at the 3G USB port, but it looks a bit 'narrow' to use a normal USB plug on ... the opening is so close to the reflecting metal plate, there is hardly any room for the plastic part of the plug.
most USB cables will fit in there OK, but many flash drives are too bulky - keep a short (and good-quality) USB2 extension cable to hand.
BTW, do not be surprised when the 3G USB socket moves slightly: it is meant to do so, so that their 3G stick can get better reception. Some people prefer to us a small dap of glue to stop that movement, as their are reports on this forum of repeated sliding leading to damaged cables.