What is SMS ?
You can send from your phone short text letters. And this is SMS (Short Messaging System).
What is SMSC ?
This is Short Messaging System Centre.
Idea is simple: when you write your SMS, select recipient(s) and send your SMS, it's send to SMSC. If you see "Message sent" ot something like that, don't worry. It means, that your SMS was delivered to SMSC and SMSC try to delivery it to recipient(s).
Why is it done this way ? Let's say, that recipient's phone is disabled. If it will done this way, that your phone will try to delivery it directly, it will loose energy during each try and you have to be in network coverage during it. GSM network makes it easier - not you, but SMSC try to delivery it. And of course, you can decide, how long it should be done (after it SMS will deleted).
What SMSC should I use ?
The most simple answer is: ask your operator and use its' own SMSC.
But sometimes it's not so simple: it's possible, that SMSC of your operator CAN'T send SMS to some other network. You should try to use different SMSC then. But remember: if you will try to use SMSC from different country, you have to have activated international calls.
Can I use my own SMSC in roaming ?
Yes.
Can SMS contains not only text ?
Of course. Each SMS contains some bytes filled with contest. Normally they're filled with chars. But of course you can decide, that they have different meaning and send +binary data this way too...
In this moment we can classify SMS to:
What is length of SMS ?
Each SMS can contains ONLY 140 8 bit chars. When you code it as 7 bit SMS, you can save 160 chars (you have 140*8 bits inside and they're divided into 7 bits) and when code as Unicode SMS, 70 chars (each char in such SMS contains of 2 8 bit chars).
It's also possible to put into each sent SMS special flag, which will mean: this is first, second, third,... part of SMS. Some phones can display this info (for example info "Linked: 1/...") or even display each SMS with such flag as one long... Such SMS are called concatenated or linked.
What is price for sending SMS ?
Ask your operator :-)
Generally you pay for EACH SMS with 140 8 bit chars. It means, that after sending Linked SMS consist of 2 such SMS, you will pay for 2. The similiar thing is with Picture Images (each of them consist of 3 SMS) and Reminders from Nokia 3310 (2 SMS).
Something it's free. When ? When you are in roaming and network, you use, write in logs, that sent SMS, when it was send ONLY over SMSC of this network (remember: you can you SMSC from your home network). Or when SMSC, you used, gives info to network about error during sending, but send it correctly !
What is price for receiving SMS ?
In many networks it's free...
What is SMS class ?
Each SMS have flag with info, what should be done with it after delivering to recipients' phone. There are 4 possiblities (classes):
What is delivery time ?
This is the time, during it SMSC will try to delivery your SMS.
What is delivery raport ?
You can know, if your SMS was delivered to recipients' phone (don't misguide it with reading !). It's free. There are two ways to do it:
What it "Reply via own centre" ?
Theoretically, when you send SMS with flag to somebody, it should be able to send answer over your SMSC. Often it doesn't work (many SMSC doesn't accept SMS from forbidden networks even with this flag).
I have error, when answer to received SMS