"Ship" is being used in the first meaning listed for it as a verb in wiktionary: to send something to someone or somewhere. In this particular context it implicitly means shipping from the manufacturer's warehouses to the shops.
"In volume" means "in large amounts"; several other answers have references for this, so I won't poach.
So overall the phrase "ship in volume" means "get into the shops in large amounts." When a product ships in volume, you will be able to find it in the stores (or at least the stores you would normally expect to find an iPad in!) The alternatives in business terms would be "ship small volumes", i.e. getting only to relatively small numbers of shops (probably specialists), and "sample" (a few "samples" of the product are available to a few major customers, but it's not available to the rest of us yet).