I ruled half at the table, but I'm having second thoughts.
The ring of the ram is an ornate ring forged of hard metal, usually iron or an iron alloy. It has the head of a ram as its device. The wearer can command the ring to give forth a ram-like force, manifested by a vaguely discernible shape that resembles the head of a ram or a goat. This force strikes a single target, dealing 1d6 points of damage if 1 charge is expended, 2d6 points if 2 charges are used, or 3d6 points if 3 charges (the maximum) are used. Treat this as a ranged attack with a 50-foot maximum range and no penalties for distance.
It calls the effect a force, several times, but otherwise doesn't explicitly state that it deals force damage or is a [force] type effect. Technically, I think its actually untyped damage by RAW, which would be halved against incorporeal creatures but bypasses all resistances, immunities, and DR.
RAI treating it as a force effect and therefore dealing full damage to incorporeal creatures also makes sense.
Both untyped and force damage effects are quite powerful, so if this is your own table I would pick one and stick with it. If its for society play, maybe someone else can shed some light on it.
Personally, I think the "force" in the description is English description, rather than a spell descriptor. The ring is Transmutation, and uses bull's strength and telekinesis, neither of which is a Force effect. I think it's using the Combat Maneuver section of telekinesis so it would be half damage to incorporeal creatures. (Not full damage, since it's not a force effect, not zero damage because the effect is magical in nature and SR applies)