Light Reading has a writeup on their revised satellite radio subscriber projections, and on the conservative side, they're estimating over 17.2 Million total subscribers between SIRIUS and XM in the next 18 months.

Based on SIRIUS' growth from July 04 - March 06, SIRIUS will be growing at a rate of 243 subscribers every hour - bringing in a total of 7.1 Million subscribers in 18 months. Based on XM's growth rate from June 04 - April 06, XM will grow at a rate of 284 new subscribers an hour. That's a total of 10.1 Million subscribers in 18 months.

Obviously, there are events that cause spikes in growth - like Stern for instance. And using numbers from mid 2004 might make hourly additions a bit more conservative than necessary, but sometimes it's nice to weigh on the more conservative side.

[Light Reading]