http://metacrawler.de/sms/ is really a great site where you can send SMS for free. Immediately after the loading of the page in your browser you get a form for a telephone number and a message. After filling up, you must still accept the terms and conditions and then you can send the SMS.
Of course you must read the terms before accepting them, at least theoretically, but I read only half of it.
The main information is that the site saves some information about you, such as IP address, because they would use it to prevent a abuse. The limit, according to the terms is 3 SMS per day and user, but only one SMS per hour. In order to prevent spam, the recipient will receive only 2 messages per day independent of whether the sender is the same, or there are different people. This is understandable, because they are not able to control the users. On the Internet you can very easily fake IP address. Normally, it is enough for this, only disconnect from Internet for a moment and then connect to the Internet again. Unfortunately you can send SMS only in Germany. Normally I do not need to send a text message abroad, but occasionally it happens and the text messages costs on my mobile service provider significantly more than those within Germany.
If you receive the unwanted sms from this website, you can block the sending of short messages to your number, you need to send an e-mail to those mentioned in the terms of use e-mail address and tell your number.
In addition, it pointed out that it also may be delayed, which is not normally happen. I sent two SMS for test today, both came immediately. I am pleased with the service actually and would like to to use it, if I will have a problem with Zelfi SMS or GMX.