twits on my phone: sending is fine, receiving doesn't work.

hi, i've set it up to get twits to my phone (t-mobile in US, CA), but i'm still not getting any. I've sent the security code to the 40404 number, and it went through. Also, my twits which sent to the 40404 always came to the web browser, and my followers do see them - no problem with this. The only problem is not getting twits from who i'm following, on my phone. I've called the T-mobile customer service, and we were discussing this issue for about half an hour. They say, there is no possibility of this being their fault (and my texting works fine by itself).
Please advice.. I do need it.
and thanks for the service anyway.