Your phone line is split into three lines two analog (normal phone lines) and one digital line (video phone, digital fax, USB ISDN, terminal adapter ISDN).
The two analog phone lines can be bonded together giving you another digital line.
You now have three phone numbers two analog and one digital but you can only use any two at once. Eg the digital line plus one analog line so you can make a phone call and surf the net at 64kbps the other analog phone line will be dead in and out going.
The two analog lines can be bonded together to give you other digital line giving you a grand total of two digital lines and a connection speed of 128kbps. By bonding both lines and using the digital your now making 2 phone calls so you will need two net accounts !!!!!
Don`t worry for gaming purposes a single 64kbps connection will do just fine for playing quake III on-line with a lower ping.
Net Speed
Is it better than a 56k modem yes no doubt about that web pages load faster e-mails and files download much quicker how fast ? I can download with a good connection to the server at 7.5k sec (single 64kbps line) 54 to 60 MBs in two hours ok its not lightning fast but its better than my old 56k modem.
Ping
Welcome to the world of on-line gaming you can now compete, the playing field is now somewhat more level you will be able to play q3 with a much better ping. Your ping will be lower but to get the most out of your BT Home Highway box you will need to install a terminal adapter like an Asus ISDNLink P-IN100-ST-D 128K ISDN Adapter this will reduce your ping.
Asus ISDNLink P-IN100-ST-D 128K ISDN Adapter.

After installing a terminal adapter my ping is 50-90 on most UK servers. I can play on Quake 3 servers in Italy with friends in Spain using ADSL connections and my ping is lower. Please see the tweaking ISDN section for the best ping.
Cost
At the moment 21.12.2002 its £75 to install then £25 a month with £3.80 call charges included. Expensive compared to ADSL yes but if like me ADSL is a couple of years away and you like on-line gaming and your wife/girlfriend would like to use the phone its the only option.