CSD

Grr.

Why do all cellular telephone carriers suck? I've spent the last few months trying to figure out how to get my awesome Bluetooth-enabled T637 working as a modem. I've been able to get it to work via GPRS (for those in the AT&T world, mMode) but that's bleeding expensive. I just wanted a simple analog connection -- so what if it only works at 9600 baud, I can handle that with a text-only mail client.

Recently I discovered something I did *not* know about modems: when you issue an ATD command, you can choose if it's voice or should be interpreted as data. Apparently this is something in the modem to route the communications either to the speaker or serial cable. Anyhow, the difference is a measly semicolon:

ATDT5551212; (voice call)
ATDT5551212 (data/fax call)

Without the semicolon, the modem tries to create a direct circuit that is supposed to be less lossy than voice calls. Thus the use for a modem (and why we can use compression). In order for this to work, the telephone switch has to support Circuit Switched Dialing (CSD). Ironically, this is a feature built into the GSM specs, so it's no burden on a carrier to implement it. Unfortunately, to pressure people into using the higher-cost GPRS service, AT&T wireless has turned it off. Bastards.

I figured since Cingular and AT&T wireless merged, that they would unify their services, but they did not. Even though Cingular customers can use CSD, former AT&T customers cannot. Bastards.

At least two of my three choice features still work:
1. Bluetooth connectivity
2. Voice calls

I'll just have to fight for number 3... or wait for someone to tell me about a "fix" ... or just use WiFi hotspots until I can switch carriers.