8G not enough on iPhone 4 options

Hi- sorry I don't know if this new-ish phone to me is CDMA or GSM (carrier is Sprint/Nextel if that helps).  I got this iPhone 4/8Gig "free" a few weeks ago but I'm finding that between the new, wonderous world of apps now open to me, and my existing music library, 8gigs is coming up short. I don't suppose there is any options increase the space in this device, without getting a whole new device?  It sure would be great if it at least had a slot for a micro card for extra storage like on my old, crappy, dumb-phone (which I could use as an oversized mp3 player... if I could only find it.)  I'm not a big fan of the new 'cloud' based solutions, as they depend on too many variables that are out of my controll, with the probablility of leaving me without my music.  Plus, the delay is anoying.  My area is lite on the available technology and cell service.  Can an iPhone 4 accept additional memory space upgrades?