We are offering "new old stock" with this product. Although proper function on an ISDN NTBA and connections with X.75 and PPPoISDN can still be established, you'll have a hard time finding a phone company that still offers the service. We are therefore recommending to see this card as the cheapest method to get a clock-port into your big box Amiga. The following is the original product description, now almost 20 years old. We kindly ask you to only buy this card for it's expansion ports, not for the ISDN functionality.
ISDN Surfer is a Zorro card for "big box" Amigas that makes a direct connection to the ISDN-S0 bus.
With the availability of broadband internet connections we see the ISDN-Surfer as a backup, in case the broadband connection does not work temporarily. It's also an inexpensive way to add a clockport to a Zorro-machine. After our remaining stock has been sold, this product will not be produced any more.
With the ISDN-Surfer, you enter the information highway the digial way, because an ISDN board allows the direct connection to your phone company's NTBA. There is no key telephone system, no modem and no terminal-adapter in the way to reduce performance. The connection is purely digital, your Amiga is directly connected to the telephone switch in your phone company's premises!
The only requirement is an ISDN phone line, that is offered by many phone companies all over Europe. All these products have one thing in common: The NTBA, the interface for digital communication devices. You can connect a digital phone, a key phone system, or a computer to it. You don't have to worry about compatibility at all: Due to the drivers being totally CE96 (Q931) compliant, we can guarantee the function in practically every European country. Even the ISDN lines of American phone companies that use an S0-NTBA are supported.
Although ISDN technology is totally different from analog modems, you won't have any problems getting familiar with it's use, because the drivers emulate a Hayes-compatible modem with an AT-command set. This enables virtually any software that can handle a modem also to go online with the ISDN Surfer (only exception: Fax-software). Special commands in the set let you use the ISDN-specific services that your phone company provides. As the most popular example, the caller identification is to mention.
This means for you: With some quick changes in the settings of the software, you can adjust your TCP/IP stack to make use of the ISDN Surfer, no matter if you are using Miami, MiamiDX, AmiTCP or Genesis. After these small changes, you can go online with 64KBit. You can even make two independant connections at a time, just like having two separate modems or terminal adapters. Your Amiga can be connected to the internet while taking another call on the other line with an answering-machine-software for example. Naturally, the ISDN Surfer only occupies only the number of channels that it really needs, leaving the bus free for other ISDN devices at the same time. This enables you to surf the net and make a call at the same time - the most popular reason for getting an ISDN line. It does not make a difference what type of telephone you use: A digital phone, an analog phone connected to a key phone system, or an analog phone connected to an A/B adapter.
The ISDN Surfer has two expansion ports: One clockport as known from the Buddha Flash and X-Surf Ethernet boards, and one 26-pin expansion port. The clockport can be used to connect a Silversurfer serial port, or a Delfina Soundcard. The 26-pin expansion port can be used for a VarIO IO card.