2G phones can still pull data, so that is not a guarantee you won't end up with data roaming charges. You could probably accomplish the same thing by just turning off 3G networks in your current phone. There may also be an option to simply turn off data. Another issue is that your Dash may not work for wifi without a SIM in it, so it would be a pain to keep moving your SIM back and forth.

I'm not familiar with your phone, but check your setting to see if you can just turn off data while roaming. It is a common setting.