3MB over a wireless connection is a lot of data.

If you must do it w/o a BES, you need to break your 3MB file into managable chunks. FYI, RIM recommends packets that are 2-3KB in size.

First, your device will need to query the server for a directory of files (aka chunks) and then request each of these files individually. If one fails, the device will rerequest the file until it has all of them. Not pretty.

One important note is that different carriers impose different max sizes for http requests/responses.

With BES, the work can be done on the server side.

Either way, you will consume a lot of battery life downloading a 3MB file.

Can you get the data onto the device in another way? Sync via USB and then just send updates wirelessly?