I think if you live near the border of home/away, then you can make roaming calls/texts while within the home zone.
With WIND, I absolutely can not do this. I've tried. I think with Mobi I might actually be able to make roaming calls/texts at my home since Mobi's coverage doesn't extend west of Mississauga. I'm not in West Mississauga but I think I might be close enough to the border since I have noticed mysterious GPRS charges from MyWallet when I was with Mobi. I changed my phone's setting to WCDMA only after that and I never had this problem again.