I also have a D3. I bought a water damaged myTouch 3G off ebay for $30. It has spots under the screen and the trackball doesn't scroll up, but it makes a great WiFi hotspot. I keep it at home and swap the SIM. I have WiFi at work, and I don't care if I only have EDGE while I'm driving around.
Word of advice... If you decide to go this route and are using the Chinese radio files, do NOT power up the D3 without a SIM card when the cellular antenna is on. You must activate airplane mode or insert a different SIM. Otherwise it will try to reactivate the CDMA antenna, which will cause an error in com.android.phone that will force you to do a restore. This happened to me and it was a tremendous PITA.