I installed SP Mobile on iPhone4 yesterday. Vanilla install connecting to a SB SOLO back at home that is AV connected to Sky+HD. The default Server in Settings --> SlingPlayer is dish.sling.com. So I would say that the default setting is indeed dish.sling.com. You should be able to ping the DNS Name for which it should reply. I am not aware of any other dish.??? Server settings.
Hope this helps.