I have gotten this to work on several small offices that we are supporting across the country, and have remote dialed into them.
Here are a couple of kickers to be successful at it.
1) Analog port 1 has to be dedicated to remote dial in. It cuts off the speech pathway if modem enabled is checked. So if you need all the analog ports for speech - its a no go.
2) You have to change the default name for remote manager. (that held me up ah hour or so)
3) Otherwise follow the job aid for setting up a dial in (it gives you step by step instructions)
The final trick that I have used is if there is an extra stations port. We will plug a station directly into Analog port 1, and then call the site ahead of time and let know next call will be modem call can you please transfer me to station XYZ (the station plugged directly to Analog port 1). You can probably get creative with programming to figure out a way for this to be automatic, but I haven't had the time yet to play with that aspect.
You may run into the issues that Morrack brought up. Dialing in and not being able to do anything - I assume is probably not being able to find the box with Manager. I have experienced this, and was able to resolve it by playing with my dial-in connections IP settings. It was on the dial in side not on the IP office. As long as you have DHCP or Dial-In server selected you should be good on the IP side.
Unfortunately do not know anything about the BRI issue - only have done it on basic systems 1-2 analog lines with about 4 users.