With most Hayes compatible modems you can use the ATX command to prevent the modem from looking for dialtone before it dials. This solves the problem of having to worry about it finding the dialtone.
It depends on the modems. Some require a dial tone and other things to originate a call. However most 'quality' modems seem to work. USR Couriers over some of our copper pairs (not BT) have been reported as being successful.
Note that not all BABT Approved modems will have approval that applies for both PSTN and analogue 'private' circuits. Also don't get smart and attempt to use an EPS-8 (four wires) as two EPS-9s (two wires) over long distances. Finally, if the presentation uses the wrong pins, you can always get an extension socket kit and wire it up the way you want.
Spectrum Cellular Corp. offer a product product, AXCELL, which interfaces with quite a few TACS (Analogue) phones including NEC P3 and OKI 900. The cost of the interface is UKP299, and you basically get a BT socket with dialtone.
It will not work with car kits (just in case you wanted the extra power boost) because they use the same socket as the car kit. However, they reckon they can get a consistent 4800 carrier over an average quality connection, and the beauty is you could plug in other BT-jack equipment, including fax machines...
AXCELL is distributed in the UK by Tele-Adapt and they can be reached on (0181) 421 4444; Fax (0181) 421 5308 (email 100111.2713@compuserve.com or colin@teladapt.demon.co.uk) Tele-Adapt are a company specialising in modem connectivity and also offer kits for connecting in various other countries.
Also, the following units have external jacks for faxes, etc.
NEC 9a, P3, Nokia - most models, Motorola - some models. Most Transportables have adapters that fit between the handset and base unit that emulate key presses. Almost all car phones (ie genuine class 2 portables) can be 'modified' for use with modems.
A recommended phone for data is an Oki model [number, anyone?] which gives an RJ-11 jack on the bottom of the phone.
The Short answer- No.
Longer answer- A modem is a device for converting digital information into an analogue wave-form for transmission (normally) over the telephone network.
GSM networks send all information in digital form, so there is no need for a modem.
But why wouldn't one work? Why not simply connect a modem into the GSM phone's audio circuitry and let it reconvert the analogue signal into digital form?
The reason is that a very clever speech coding algorithm is used in GSM. It has to be clever, in order to squeeze intelligible speech into 13 kbit/s. The coding scheme is called Regular Pulse Excitation-Long Term Prediction (RPE-LTP). RPE-LTP only works because speech contains a lot of redundant information, so a lot of the signal can be thrown away. Subjecting a non-speech signal (like a modem tone) to RPE-LTP will result in a distorted mess.
Try listening to music via a GSM phone... pretty unmusical, isn't it?
So in theory it won't work. In practice, there are unconfirmed reports of some success by strapping an acoustic coupler to a Mercury One-2-one phone. But I stress that these reports are unconfirmed, and personally I remain sceptical.
[{*} Someone emailed the following
so that seems to clear it up] We tried this by direct wiring into a handset! The results were awful! :-)
A 300bps/baud connect was possible but with so much noise it just wouldn't
hold. The main problem actually seemed to be RF breakthrough from the
transmitter but the coding couldn't have helped much! :-) Anyway it's
not worth thinking much about.. :-( If you live under a base station so the
phone drops to very low power it might just work... Anyway most ISP's
won't let you login at less than 2400 :-/
Having told you what won't work... what is the answer to what will work? What you need is a data adaptor that enables the digital stream from your PC to be fed directly into the GSM phone. Such devices are currently very expensive (eg the Nokia PCMCIA card), but prices will surely fall. Equipped with such a device it is possible to send 9600 bit/s error-protected data via a GSM network (if your network offers a data service). The network will have an "Interworking Function", otherwise known as a bank of modems, that will enable you to make calls to normal PSTN modem-based services.
Problems have been experienced with misbehaviour of Modems on Mercury and not BT and vice versa. The problem can be due to synchronisation errors. The clocks free-run until a little slice of time disappears as they resynchronise; that does for V.32bis modems.
Other reasons involve not automatically adjusting levels (auto gain control- AGC).
If you are sure that it is not your modems or set up (and BT via 150/152 doesn't help), try contacting one of the following for more information Derek Woodroffe (Mercury) on (0116) 265 2068, or try Andy Lichfield (0171) 356 9324, Mike Jennings (0171) 356 9169, or Mick Eames (01426) 923607 (last three people BT). Be NICE to them! They've successfully helped others in the past.
You may also experience problems on international connections. Normally, speech channels on international circuits are cut from 64K to 16K - this is ok for speech: you are unlikely to notice any degredation. However a fast modem would see a lot of information disappear. BT do have some equipment installed at Madley Communications Centre near Hereford (where over 30% of international traffic is handled) that recognises Fax and Modem traffic and routes it through non-compressed channels, and the detection of Modems and Faxes is now full automatic on most (if not all) compressed routes.
Additionally there is a new (V.8) protocol used with V.34 to clearly announce to the network that this is a V.34 modem call, and hence to allow it to optimise the call setup.
BT's national network uses 64K channels everywhere so you shouldn't get any problems added on long distance routing - any noise should just be from the local loop or an old local exchange.