The problem with e-mail order is its not gaurenteed. e-mail queues up in a buffer and typically goes through anti spam and anti virus scanners which may delay processing of individual messages depending on how those process the threads. So that couple happen in this example is the longer of the two messages would take slightly longer to pass though so you culd end up with:
The messages are time stamped so could in theory be reassembled to indicate a message. The SPOT device though has been designed to minimise the amount of Satellite bandwidth for eath SPOT device with the company running the SPOT system paying others for the satellite time.
I doubt whether the GPS position and the messaging information sent over the Satellite network would be more than 20 bytes in length. The GPS positional information and time stamp data could be sent using about 16 bytes. The SPOT unit serial number may be only 28 bits (3 Bytes and a Nibble) in length and the messaging system 2 bits with a couple of error correction bits (the other Nibble to make up the last byte). Overall the SPOT system isn't designed to send text messages but to just send the GPS and message data in the most compressed reliable format. Sendind a bit by bit message contained within the 20 or so byte format container packet isn't very efficient. The SPOT device is only capable of around 1900 messages before the batteries run out.
If composing an SMS text message on a possible future SPOT device then length of the text message would be around 140 bytes in length compared to the 20 or so bytes for each GPS update message currently sent. So one SMS text message will use the data bandwidth of around 7 GPS update messages. The designers of SPOT probably thought long and hard whether to include an SMS facility; the deciding factor was probably the overriding cost savings i.e. the initial market price point and the business model for the administration of the income stream or even the possibility that to gain access to the satellite network they had to demonstrate that the SPOT device would not specifically offer competition to SMS messaging services already available on the satellite constellation. It wouldn't take much to add a simple 1 or 2 line 16 character LCD display and a simple keypad to enter the SMS message into a future SPOT in addition to the current features. The problem then becomes the pricing mechanism to pay for the SMS messages.
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