I'm not sure if a library exists to help with this or not, but you can just POST some XML to an address right? What support do you need besides basic HTTP messages?
NSURL *pUrl = [NSURL URLWithString"http://dev.transclick.com/translation/xmlrpc2me?"];
NSMutableURLRequest* pRequest = [NSMutableURLRequest requestWithURLUrl cachePolicy:NSURLRequestUseProtocolCachePolicytimeoutInterval:60.0];
NSString* pStr = [[NSString alloc] initWithString"<?xml version='1.0' encoding='UTF-8'?><methodCall><methodName>authentication.signin</methodName><params><param><value><string>username</string></value></param><param><value><string>password</string></value></param></params></methodCall>"];
NSData* pBody = [pStr dataUsingEncoding:NSStringEncodingConversionAllowLossy];
[pRequest setValue"text/xml; charset=utf-8" forHTTPHeaderField"Content-Type"];
[pRequest setValue:[NSString stringWithFormat"%d", [pBody length]] forHTTPHeaderField"Content-Length"];
[pRequest setHTTPMethod"POST"];
[pRequest setHTTPBodyBody];
m_pUrlConnection = [[NSURLConnection alloc] initWithRequestRequest delegate:self];
NSXMLNode and NSXMLDocument are not supported on iPhone device
// Create the request
NSMutableURLRequest *request = [[[NSMutableURLRequest alloc] init] autorelease];
[request setURL:[NSURL URLWithString:@"http://www.shacknews.com/extras/post_laryn_iphone.x"]];
// Set request body and HTTP method
NSString *usernameString = [LatestChattyAppDelegate urlEscape:[[NSUserDefaults standardUserDefaults] stringForKey:@"username_preference"]];
NSString *passwordString = [LatestChattyAppDelegate urlEscape:[[NSUserDefaults standardUserDefaults] stringForKey:@"password_preference"]];
NSString *bodyString = [LatestChattyAppDelegate urlEscape:postContent.text];
NSString *parentId = [NSString stringWithFormat:@"%d", parentPost.postId];
if ([parentId isEqualToString:@"0"]) parentId = @"";
NSString *postBody = [NSString stringWithFormat:@"body=%@&iuser=%@&ipass=%@&parent=%@&group=%d", bodyString, usernameString, passwordString, parentId, storyId];
[request setHTTPBody:[postBody dataUsingEncoding: NSASCIIStringEncoding]];
[request setHTTPMethod:@"POST"];
// Send the request
NSHTTPURLResponse *response;
NSString *responseBody = [[NSString alloc] initWithData:[NSURLConnection sendSynchronousRequest:request returningResponse:&response error:nil]
encoding:NSASCIIStringEncoding];