While similar to cart ponies in many ways, ponies that are trained and work as a team to pull carts must have a significant amount of additional specialized training beyond that of other cart ponies. Cart ponies that work as team are nearly always two legged ponies, and almost always have matching, aesthetically pleasing tack. Moreover, the ponies that make up a team are usually chosen to of similar height and overall physical build.
There are very few (to my current knowledge) multiple pony cart teams in ponyplay. This is most likely due to the difficulty not merely in finding multiple ponies, but in the regular group training required to facilitate safe and smooth operation of working together. However, it is quite a sight to see a team of rubber catsuit clad ponies in full tack working together to pull a sleigh in fresh white snow!
The ponies making up a carting team will usually have been previously trained in pulling carts individually prior to joining the team. Moreover, each member of the pony team will have extensive experience in ponyplay in general and will be proficient in rein and whip/leg aids, and of course will be comfortable working in ponyplay tack often including working with their upper limbs in restraints (though cart ponies usually do not work in hoof boots).
Team carting in ponyplay requires much additional training beyond learning to pull a cart. All ponies that form part of the team must be synchronized on their movements to be able to pull the cart successfully and safely. This requires regular training of the ponies as a team, which can be quite difficult from a logistical point of view. Moreover, the space required to train a pony team confounds these issue further.
Hence, team carting in ponyplay can be quite the sight, and the obvious commitment of the ponies and their trainers by itself warrants a special category.