i used both iphone before and currently using blackberry curve. I love the blackberry. Iphone is very fancy... and nice looking and cool function but i think blackberry is much more reliable.. because for my iphone I wont get any sms when I have a voice message cos iphone couldnt recongize the phone number format for voicemail box..
I think iphone is ok for email if you dont have too much to receive and reply.
While blackberry is not so fancy but the curve looks good and light. and it is reliable and i love the instant email !!
There must have been a problem with your particular phone, then, because I have no problems getting texts when I have voicemail also. One should not affect the other.
Also, IMO, iphone is better for email in that you get full html email on it (pictures and stuff) whereas on the blackberry, currently that is not supported, so emails look like a sea of links and gibberish. To me, wading through all of that mess to get to the actual email was very frustrating.