The majority of their satellites just bounce the signals back down to a nearby ground station. Their version 1.5 sats, which they started launching about a year ago, include laser links to allow sat->sat communication. Their plan is for the remaining 3/4th of their fleet to have laser links.
One interesting side-effect of the laser links is that they can open up connections between stock exchanges and trading houses that are faster than direct fiberoptic lines. Milliseconds count in high frequency trading.