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Send and Receive SMS Text Messages Using a GSM GPRS Wireless Modem

If you need the ability to send SMS text messages from your website or Internet connected software, you will quickly discover several options such as using the free wireless carrier email to SMS gateways (ex. 5555551212@vtext.com), third party SMS gateways (ex. CellTrust HTTP API), direct connection to SMSC’s (after days of research and phone calls to AT&T, we couldn’t figure out how to do this), and GSM GPRS wireless modems.

The free SMS gateways are great if you know both the phone number and mobile carrier, and you don’t require delivery to or from a short code.  If you don’t know the mobile carrier you can look it up through any number of free or paid third party API’s (CellTrust offers one).  If you need to use a short code, then third party SMS gateways are your only choice. But at large volumes, the cost can really add up. GSM GPRS modems are the best choice if you need to send high volume, don’t know the carrier, and don’t need a short code. However, programming and scaling GPRS modems can be a challenge because you have to use AT commands that aren’t always implemented in a standard format and you also have to do deal with serial port communication (For a great tutorial, checkout: http://www.developershome.com/sms/). If only somebody made a GSM GPRS modem attached to a web server…. Somebody did, and I have to give it a very positive review.

We stumbled upon the SMSFinder while on a tech support call with Multi-Tech. We had purchased a GSM GPRS modem and we intended on programming it using AT commands to send and receive text messages. We found out from our very helpful tech support person (Multi-Tech support is excellent btw), that if we just wanted to send text messages, the SMSFinder is for us. The SMSFinder is a GPRS Wireless Modem, with an ethernet port, wrapped with a web server. Just slide in an active SIM card, plug it in, and your ready to go. It exposes a simple HTTP API for sending messages, along with a basic GUI web admin portal. The device handles queuing the requests if it gets behind. We have put multiple modems behind a load balancer, assigned it a VIP, and instantly have the ability to scale. The downside to this approach is that your messages will come from one or more phone numbers, not short codes. But if you need to inexpensively send a large volume of messages very cheaply (10,000 messages via a third party api will cost you about $500), and you don’t require a short code, then you should consider the SMSFinder.

Here’s a short summary of options for sending SMS test messages.

And one more thing, Multi-Tech is releasing a 4 and 8 port version in Summer of 2009.

May 31, 2009 - Posted by Keith Forsythe | SMS