I have several gmail accounts on BIS which show up instantly and conventional accounts (from my ISP's) which take a few minutes longer. I agree with the comment that changing devices is not going to fix your problem. I would ask the following questions:
1. What OS are you using. If you are not at at least .75, fix it
2. Have you asked your carrier this question?
I seriously doubt that the problem is BIS.
Another suggestion: Try creating a GMail account and see what happens. 73