Has anyone found more detailed terms for Swisscom's iPhone abos? I'm trying to find out whether you can down/upgrade between them.

According to Swisscom's general natel subscription FAQ, one can do so freely, except for downgrading within the first 6 months, in which they charge you 95 CHF for the privilege.
This can hardly be true for the iPhone abos though, since the cost of paying a more expensive monthly charge would more or less cancel out the subsidy after 6 months.