Well Samsung Blast is a Regular Everyday phone good for anybody, but the Shadow 09 is a Smart Phone like a PDA or Pocket PC which has lots more features like Windows Mobile which is good if you do alot of work on the go, but just for a phone and media go with the Blast.
As far as for messaging purposes you'll want to go with the blast because its a lot cheaper especially if you buy it online (free) and the messaging will be virtually the same. But if you want the added features you'll want to go with the shadow but I doubt you'll get to use many features without paying extra money for it. Go with the blast