I got this as a commment on one of the community blog posts today. I thought I'd post it here so you all have a chance to comment too. I'll post a response soon.

Hi! My name is Chris and I work at Help.com. One of our members posted a question and after reading your site I thought you might have the expertise give some guidance to this person. Their question:

"How do I text a message to somebody's cell phone from my computer? Does VoIP allow this to happen?"

This one came in and I confess some inability to answer. I'll take my best guess at this, but I am really just guessing. I don't have any firsthand experience in implementing an SMS gateway.

A few weeks ago, on my personal blog, I posted IM, SMS and Business Use in response to a post by Dan Taylor about the business case for IM. That generated enough interest that I followed up with More on SMS and Business Use as a result of some email from an interested reader.

I admit I use SMS, but not wildly. I'm no SMS power user, yet alone an implementor. But I do know a little about SMS, The question sent me off on a brief search.

---

Here's some information from Wikipedia about SMS:

Short Message Service (SMS) is a service available on most digital mobile phones that permits the sending of short messages (also known as text messages, or more colloquially SMSes, texts or even txts) between mobile phones, other handheld devices and even landline telephones. Other uses of text messaging can be for ordering ringtones, wallpapers and entering competitions.

Technical details

The Short Message Service - Point to Point (SMS-PP) is defined in GSM recommendation 03.40. This is separate from GSM 03.41 which defines the Short Message Service - Cell Broadcast (SMS-CB) which allows messages (advertising, public information, etc.) to be broadcast to all mobile users in a specified geographical area.

Messages are sent via a store-and-forward mechanism to a Short Message Service Centre (SMSC), which will attempt to send the message to the recipient and possibly retry if the user is not reachable at a given moment. Both Mobile Terminated (MT), for messages sent to a mobile handset, and Mobile Originating (MO), for those that are sent from the mobile handset, operations are supported. Message delivery is best effort, so there are no guarantees that a message will actually be delivered to its recipient and delay or complete loss of a message is not uncommon, particularly when sending between networks. Users may choose to request delivery reports, which can provide positive confirmation that the message has reached the intended recipient, but notifications for failed deliveries are unreliable at best.

Transmission of the short messages between SMSC and phone is via SS7 within the standard GSM MAP framework. Messages are sent with the additional MAP operation forward_short_message, whose payload length is limited by the constraints of the signalling protocol to precisely 140 bytes. In practice, this translates to either 160 7-bit characters, 140 8-bit characters, or 70 2-byte characters in languages such as Arabic, Chinese, Korean, Japanese or Slavonic languages (e.g. Russian) when encoded using 2-byte UTF-16 character encoding (see Unicode). This does not include routing data and other metadata, which is additional to the payload size.

Larger content (known as long SMS or concatenated SMS) can be sent segmented over multiple messages, in which case each message will start with a user data header (UDH) containing segmentation information. Since UDH is inside the payload, the number of characters per segment is lower: 153 for 7 bit encoding, 134 for 8 bit encoding and 67 for 16 bit encoding. The receiving phone is then responsible for reassembling the message and presenting it to the user as one long message. While the standard theoretically permits up to 255 segments, 3 to 4 segment messages are the practical maximum, and long messages are billed as equivalent to multiple SMS messages.

Short messages can also be used to send binary content such as ringtones or logos, as well as OTA programming or configuration data. Such uses are a vendor-specific extension of the GSM specification and there are multiple competing standards, although Nokia's Smart Messaging is by far the most common.

Some service providers offer the ability to send messages to land line telephones regardless of their capability of receiving text messages by automatically phoning the recipient and reading the message aloud using a speech synthesizer along with the number of the sender.

External Links

• Free SMS for Firefox (Google powered)
• SMS Forum
• SMS, the strange duckling of GSM (PDF format)

---

I've seen a fair amount of mention of SMS gateways for corporate networks in the past. I know there are a few accessible out on the net. It would seem to me that it's even a logical component of the popular Blackberry Enterprise Server, although I don't see any mention in the limited documentation I have.

I know the recently visible Jajah proclaims it's a Skype killer in VoIP and can do SMS. I'd argue it's a web service that isn't really VoIP. And the SMS integration is via browser, not via VoIP at all. While a Google search yielded a lot of results, most weren't really VoIP solutions and didn't provide any great ideas.

A Google search yields a lot references to both VoIP and SMS. It appears to be supported with some modules for Asterisk, but I've no direct exposure to that. Skype apparently added SMS support over a year ago, but I've never noticed or used it, and Skype isn't in general business use by large companies. SysMaster has an SMS Gateway listed under VoIP products. That was the most tangible off-the-shelf solution in my quick search.

I'd expect that some of the recent integration efforts with Customer Relationship Management (CRM) software and VoIP would bring in some SMS capabilities as well, but I couldn't find a clear strategy among CRM software providers.

I'm going to close with thanks to Chris for bringing a puzzling question for which I don't have a good answer. I'm responding via email, this blog post and a post in the Realtime VoIP Community forums. If anyone has a really strong answer to the question, I'd like to hear it. Please jump in with comments here or voer in the forums.

Technorati Tags: VoIP, SMS, reader question