for breaking up the t-1, you could use something like an Adtran Total Access 600 Series. you can order one with a t-1 wan link and a DSX-1 on the back (model 4213612L1#TDM). The DSX-1 interface allows you to signal as a T-1 to another device (your t-1 line card in your asterisk box). they also have an ethernet and a v.35 interface. when you setup the device, you can map specific channels to different interfaces.
the model number above is for a 12-port FXS config, but it is the lowest model that i know of that supports the DSX-1 on the back. you obviously wouldn’t use the FXS in this case because of the t-1 to the asterisk box. if you wanted to use the FXS, you would use the FXO cards for asterisk. the adtran model number indicates the maximum number of FXS ports it will support, but you don’t have to use any of them. you can use a TA624 and never use an FXS port, so there is no lower limit. if you need FXS, pick one that will allow you to grow.
as for the data, you have the option to run it through the adtran’s internal router to the ethernet, or to map those DS0s to the v.35 interface. the ethernet will be cheaper if you don’t have a serial router and you can definitley plug that ethernet into a firewall or extrernal router (it just adds another layer 3 hop).
i would ask your service provider, as they may already provide an iad for you. one tip i’d mention is that the D-channel on a PRI usually has to be on the 24th DS0 (from the telco side – not sure about asterisk). also, make sure they’ll do frac PRI for you (ie. chan 1-10 for IP, 11-23 for PRI-B, 24 for PRI-D), as many providers don’t.
you can configure this without PRI if you need to, although you may lose PSTN features. ask your telephone company about that.
regarding the fax, if you wanted to use something other than asterisk to handle your fax line, you could use one or two DS0s on the T-1 just for fax and map them in the adtran to the FXS interface. if you do this, you’ll need an amphenol cable/connector for the wiring.
hope this helps. good luck!