Was asbestos used within wallboard itself, or just in the joint compound?
The short answer is: yes, wallboard can contain asbestos, but it's unlikely. The reason is that regular gypsum drywall panels had a decent fire rating, unlike the seam joints, which would have to be finished with a fire-proofing material, as asbestos (I say had as during the times when they used asbestos, up until the mid 80s) .  You're very likely to find asbestos-containing panels around fireplaces and in floor tiles, but it would have been unnecessarily expensive to do entire walls out of asbestos-containing sheets.

Other places you may find asbestos (from the Georgia Environment, Health and Safety Department website):


STEAM PIPES, BOILERS, and FURNACE DUCTS (insulated with an asbestos blanket or asbestos paper tape) 
RESILIENT FLOOR TILES (vinyl asbestos, asphalt, and rubber), the backing on 
VINYL SHEET FLOORING, and ADHESIVES used for installing floor tile. 
CEMENT SHEET,MILLBOARD, and PAPER (used as insulation around furnaces and woodburning stoves)
DOOR GASKETS in furnaces, wood stoves, and coal stoves. 
SOUNDPROOFING OR DECORATIVE MATERIAL sprayed on walls and ceilings.  
PATCHING AND JOINT COMPOUNDS for walls and ceilings, and TEXTURED PAINTS
ASBESTOS CEMENT ROOFING, SHINGLES, and SIDING.