The default timeout limit is 120,000 milliseconds (2 minutes). And is configured on the service providers servers or the BES server if your on a corporate service. They also limit the amount of data you can send . If you need more contact your IT group or service provider and discuss this with them, Dont be surprised they either dont know what your talking about or refuse.
Link to an example
KB24660-How to configure the timeout limit for HTTP connections for BlackBerry smartphones in BlackBerry Enterprise Server version 5.0