We're not pleased that the T-Mobile G1 lacks a standard 3.5mm headphone jack, but there are ways to use your favorite headphones with the smartphone. The Seidio Mini USB to 3.5mm Adapter is a simple accessory that attaches into the G1's mini USB port and has a 3.5mm jack on the other side where you can plug in your headphones. The Seidio Mini USB to 3.5mm Adapter costs $9.95.