There are hundreds of offers in Internet that promise you free sms. I think, GMX is one of those services that you could really use for that.
If you want to send free sms, you must register an “GMX Free Mail Plus” account and give your bank account information. It is necessary for the cases if you send more than 10 sms monthly and GMX are able than to receive a money for those sms via debit.
In addition, you must be aggrieving to receive a newsletter with commercial offers from partners of GMX.
I’m using GMX-services more than one year and I haven’t yet any problems.
But if you want to communicate via sms on the way, you can try “Free SMS” from Zelfi.