What Printing Methods Does Threadless Use?

Normally I would think that a DTG imprint would be best for this logo, however the materials which make up this shirts are not good for DTG, possibly an ink jet transfer would work.

on the Threadless site, for each design it states what method and how many colors are used. the majority seem to be screen printed.

here's a good site that explains simulated process as well as several other separation techniques.
FAQ -=> Artwork

nice design btw!
for your personal stuff, if you're doing small volume i'd suggest looking at quality DTG printing on darks. DTG would be more cost effective on small runs.

Look into a good printer who uses a 4 color process

I disagree on the four color process, because on anything but white, you are going to have a white base with translucent inks on top (CMYK inks are translucent). Simulated process is the way to go...and to be reasonable in price you are going to order over 144.
7 colors is a standard for an 8 color press (one station will be flash) and to truly get a wide gamut, you will need a 12+ color machine, with 2 flashes in. Simulated process standard had 9 colors for separations (software default). However, I use photoshop to make my own as I have found that 80% of the time spent in with the simu process software tweaking colors. Just easier in photoshop for me.
BTW - to truly get great prints requires a dedicated shop with a lot of high end screen systems, outstanding prepress dept etc...all to capture the dot, print the dot and blend the dots for a wide range of color...things we do at Legends everyday!
hope this clarifies somewhat