1) Is the PHP code obfuscated on the SMS FoxBox?

NO,  SMS FoxBox is opened for customization so you can edit all the code of the GUI to fit your needs

2) How can I write SMS foxbox "plugin" for my work?
You can use BASH scripting, C or PHP  look at the tutorial section

3) Are MMS supported?
We are going to release an extension KIT to handle MMS, as you can see in the news MMS BOX is coming soon!

4) How about costs and performance of sending and receiving?

If you send a few SMS each hour, the SMS FoxBox  is the best solution for you to build a very stable SMS Gateway.

But if you send thousands of SMS each hour you have to consider to use a SMSC large account that will be soon supported by the box.

When you send a message with SMS FoxBox, you have to pay exactly the same price as when you send normally with your mobile. Most phone network provider take a fixed price per SMS and also offer tarrif options to lower the price. You can save a lot of money by selecting the right tarrif for your SIM cards.

SMS foxbox works with a "normal" SIM so the carrier availability/traffic can affect performance, I can give you peaks:

INCOMING MESSAGES: more than 30/min
OUTGOING MESSAGES: 20/min

The system does not work as KANNEL (famous open source SMS gateway that uses AT+CNMI indicator for the incoming notification), SMS FoxBox use in first place the carrier then the SIM memory as buffer so it can retrieve lot of parallel messages.