Problem Encoding to ISO-8859-1

[iamlost]

Hi

I'm trying to encode string to ISO-8859-1 and after send this data to a webservice.

I'm using VB.NET 2008.

I have the next code. It runs fine excepts the character +

baseurl = "http://www.myweb.com/api/sendsms.php"
            client = New WebClient
            client.Headers.Add("user-agent", "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.2; .NET CLR 1.0.3705;)")
            client.QueryString.Add("user", user)
            client.QueryString.Add("password", pass)
            client.QueryString.Add("alias", myAlias)
            client.QueryString.Add("dest",  mobile)
            textoSms = Me.mmTexto.Text
            textoSms = System.Web.HttpUtility.UrlEncode(textoSms, System.Text.Encoding.GetEncoding("ISO-8859-1"))                
            client.QueryString.Add("message", textoSms)
            data = client.OpenRead(baseurl)
            reader = New StreamReader(data)
            s = reader.ReadToEnd()
            data.Close()
            reader.Close()

Example:

original string: 50+50
string encoded to iso 8859-1: 50%2b50
webservice receives: 5050

Any help?