What you can do is one of these 2 alternatives:
Supposing you had Telecom Personal, like I do.
Anyone in the world can get into their website and send you a FREE TEXT SMS via the internet!! (I think YOU are charged for the message.)
Top of main page has the following link to SMS page:
(But it isn´t working right now.)
Speed and reliability should be OK since it goes straight into the same company´s system.
Another way is to send an e-mail to the cell-phone-which gets it as an SMS message.
For Movistar I know that the format is:
<código de área sin 0 ni 15> <nro de movistar> @sms.movistar.net.ar
Again RECEIVER pays the SMS but at local, NOT INTERNATIONAL, rates!!
What you need to do now is check for the correct procedures and webpages for YOUR local SERVICE PROVIDER and for your friend´s providers abroad.
Hope this works for you!
PS: most newer cell phones can send e-mail straight from phone