Sending SMS overseas

[seamonkey]

Hi,
Just a question about trying to send my friend (in the Phillipines) a SMS. However I try to do it - despite definately having an accurate number, Exetel wont allow me to. When I do it via the website it just rejected immediately.

"This message cannot be sent. The destination mobile number is not available."

Whatever combination I try it doesn't work
Ive tried through a service I have with Pennytel. No problem whatsoever. Any ideas?

TIA

[Himantha]

Could you please PM me the problem destination numbers, enabling us to investigate.