Here is a simple tutorial for Minoan horns. A few of tips in regard to subD modelling first.

• Since each subD level quadruples the number of poly's, use it wisely.
• Test the model at various levels and use the lowest level possible to achieve required results.
• Move up and down subD levels as you model. You can view the smoothing in higher levels and achieve faster program response in the lower levels.
• If your program allows subD to be applied to selections instead of the entire model, do this as appropriate.
• Save a copy of the model before refining the control mesh.
• Subdivision works most predictably with quads. Avoid triangles and ngons as much as possible.
• Aviod nonmanifold geometry when using subdivision. Nonmanifold geometry exists in many forms. The most common example of nonmanifold geometry is that of 3 or more faces sharing a common edge.

SubD Modelling Minoan Architectural Horns
1		2
Create a cube.		Select green face and face on opposite side.
5		6
Scale size of cube upwards.		Keeping same faces selected, extrude them.
7		8
Select green faces as shown.		Extrude selection.
Creation of new geometry is complete at this point. Next is using subD techniques to tweak the form.
9		10
Just a test to show what the model looks like at level one subD. Looks too much like a pillow. Next steps will fix this.		Select hi-lighted edges and those corresponding on opposite side of model. Crease edges.
11		12
Subdivide to level one.		Subdivide to level two.
13		14
Subdivide to level three.		Select green faces and move upwards to refine shape.
15			Once satisfied with the shape, commit or refine control mesh. This converts subdivision to a wireframe so model can be exported and used in programs which doesn't support subD. This will create poly's which aren't needed. If low poly models are required, set the model at the lowest subD level. Then after refining the control mesh, consolidate redundant poly's. If the horn model is to be a detail of a larger model, subD level one will probably be sufficient if you use a phong or similar smoothing algorithm. In AC3D, this is called crease angle.
Model can be tweaked further at this stage.
This portion is to show how to create the same model when the command crease edge is not available. For instance, the program AC3D does not save edge information with the model so creasing an edge is not available.
8a		9a
Recreate the model up to step 8.		Select edges hi-lighted and corresponding edges on opposite side of model.
10a		11a
Apply small bevel to selection.		Subdivide to level one.
12a		13a
Subdivide to level two.		Subdivide to level three.
14a		15a
To tighten radius, select edges shown and move up.		To control the radius of the subdivision, add edge loops and move them close together. Bevelling is one method of accomplishing this.
16a
Tweak model as desired. Refine control mesh when satisfied.