Section 5.1. Pricing: Paying for SMS Messages
SMS Fundamentals > Pricing: Paying for SMS Messages
Chapter 5. SMS Fundamentals
When SMS was originally designed, it was not intended for person-to-person messaging. Instead, it was conceived as a means of delivering a service-based message to the user, such as a voicemail notification. As a result, the signaling channel of the GSM system was used, and the architecture not optimized for the kinds of messaging we do today.
A text message is limited to 140 bytes, or 160 7-bit characters, though languages that require 16-bit encoding will be limited to 70 characters.
When an SMS message is sent, the mobile phone uses the configuration data found in its SIM card to locate and contact the Short Message Service Center (SMS-C) operated by the carrier. The sender's carrier will forward the message on to the recipient's carrier using SS7 signaling protocols, and the recipient's carrier holds the message until it can be delivered on to the recipient's phone, as shown in Figure 5-1.
Figure 5-1. SMS network architecture simplified
The fact that the message must cross so many networks can lead to low reliability in the system: delivering SMS messages across carriers is more likely to fail than delivering messages within a carrier's network.
It is worth noting that "true" SMS exists only on GSM networks. GSM is the system used by carriers across most of the world, but in the United States, several carriers (including Sprint and Verizon) use an alternative system, CDMA.
This is unlikely to impact you directly, as CDMA-based carriers have created their own SMS-like systems and interface directly to GSM carrier's SMS system. You may notice, though, some idiosyncrasies when sending and receiving messages from these carriers. For example, Sprint phones will typically allow users to compose 220 character messages, rather than 160.
5.1. Pricing: Paying for SMS Messages
In the United States, an SMS message is charged to both the sender and the receiver. Pricing varies by carrier and plan, but typically a message will cost a consumer $0.10 to send and to receive (although some carriers offer "all you can eat" unlimited flat rate plans).
In Europe, Asia and elsewhere in the world, only the sender of the message pays, it is free to receive unlimited text messages. Messages can cost anywhere from 0.03 to 0.14.
