The Broadband2Go prepaid data plans from Virgin Mobile that look almost reasonable. The prices are pretty high but the prepaid plan should prevent your robot from from bankrupting you when it starts downloading robot porn or watching YouTube videos all day long.
Iridium data seems useful for robotics projects that are literally anywhere on earth. On the downside there is a price to pay for being able to get telemetry from anywhere.
On the other hand, maybe a HAM Radio approach to telemetry might work out better.