>Frankly, you may be right. I think you can duplex them though to get 256K but, then again, I'm no telcom dude.
>

I am; BRI, the basic ISDN interface, is composed of 2 64Kbit B channels + a 16Kbit D channel for control signalling - it offers rates of upto 64Kbps (in the US, this is limited to 56Kbps by some signalling restrictions) or duplex two channels for 128Kbps (112Kbps).

Unlike 56K dial-up, the same data rate is supported for uplink and downlink on ISDN; for standard POTS 56K modems, inbound data from a specialized "server" modem can be at rates up to 56K, but outbound data uses V.34 protocol - 33.6Kbps max. Normal modem to normal modem using 56K modems is V.34 - 33.6Kbps max bidirectional is the highest rate supported.

There are other ISDN options than BRI; typically, they're extrememly expensive compared to similar rates offered via xDSL and broadband (cable modem) options.

>>>ISDN lines can operate at different speeds, too: 128 and 256K
>>
>>I thought ISDN only operated at 64K (single channel) and 128K (dual channel).