Thanks to a suggestion from the Palm forums, I have managed to call webOS's email system from GLBasic, allowing me to send attachments :
INLINE
?IFDEF WEBOS
extern "C" unsigned int __stdcall PDL_ServiceCall(const char *uri, const char *payload);
extern "C" int __stdcall sprintf(char* str,const char* format,...);
?ENDIF
ENDINLINE
FUNCTION sendEMail%:file$
?IFDEF WEBOS
INLINE
char sz1[] = "{ \"id\":\"com.palm.app.email\", \"params\": { \"summary\":\"Converted Graphics\", \"attachments\": [{ \"fullPath\": \"%s\" }] } }";
char szParams[512]={0};
sprintf(szParams, sz1, file_Str.c_str() );
PDL_ServiceCall("palm://com.palm.applicationManager/launch", szParams );
ENDINLINE
?ENDIF
ENDFUNCTION