How to save a mesh in runtime on android

 using UnityEngine;
 using System.Collections;
 using System.IO;
 using System.Text;
 using System.Linq;
 
 
 public class Exporter : MonoBehaviour {
 
     private static int StartIndex = 0;
     
     public static void Start()
     {
         StartIndex = 0;
     }
     public static void End()
     {
         StartIndex = 0;
     }
     
     
     public static string MeshToString(MeshFilter mf, Transform t) 
     {    
         Vector3 s = t.localScale;
         Vector3 p = t.localPosition;
         Quaternion r = t.localRotation;
         
         
         int numVertices = 0;
         Mesh m = mf.sharedMesh;
         if (!m) {
             return "####Error####";
         }
         Material[] mats = mf.GetComponent<Renderer> ().sharedMaterials;
         
         StringBuilder sb = new StringBuilder ();
         
         Vector3[] normals = m.normals; 
         for (int i=0; i<normals.Length; i++) // remove this if your exported mesh have faces on wrong side
             normals [i] = -normals [i];
         m.normals = normals;
         
         m.triangles = m.triangles.Reverse ().ToArray (); //
         
         foreach (Vector3 vv in m.vertices) {
             Vector3 v = t.TransformPoint (vv);
             numVertices++;
             sb.Append (string.Format ("v {0} {1} {2}\n", v.x, v.y, -v.z));
         }
         sb.Append ("\n");
         foreach (Vector3 nn in m.normals) {
             Vector3 v = r * nn;
             sb.Append (string.Format ("vn {0} {1} {2}\n", -v.x, -v.y, v.z));
         }
         sb.Append ("\n");
         foreach (Vector3 v in m.uv) {
             sb.Append (string.Format ("vt {0} {1}\n", v.x, v.y));
         }
         for (int material=0; material < m.subMeshCount; material ++) {
             sb.Append ("\n");
             sb.Append ("usemtl ").Append (mats [material].name).Append ("\n");
             sb.Append ("usemap ").Append (mats [material].name).Append ("\n");
             
             int[] triangles = m.GetTriangles (material);
             for (int i=0; i<triangles.Length; i+=3) {
                 sb.Append (string.Format ("f {0}/{0}/{0} {1}/{1}/{1} {2}/{2}/{2}\n", 
                                         triangles [i] + 1 + StartIndex, triangles [i + 1] + 1 + StartIndex, triangles [i + 2] + 1 + StartIndex));
             }
         }
 
         for (int i=0; i<normals.Length; i++) // remove this if your exported mesh have faces on wrong side
             normals [i] = -normals [i];
         m.normals = normals;
         
         m.triangles = m.triangles.Reverse ().ToArray (); //
         
         StartIndex += numVertices;
         return sb.ToString ();
     }
     
     public void DoExport(bool makeSubmeshes)
     {
         
         string meshName = gameObject.name;
         string fileName = Application.persistentDataPath+"/"+gameObject.name+".obj"; // you can also use: "/storage/sdcard1/" +gameObject.name+".obj"
         
         Start();
         
         StringBuilder meshString = new StringBuilder();
         
         meshString.Append("#" + meshName + ".obj"
                           + "\n#" + System.DateTime.Now.ToLongDateString() 
                           + "\n#" + System.DateTime.Now.ToLongTimeString()
                           + "\n#-------" 
                           + "\n\n");
         
         Transform t = transform;
         
         Vector3 originalPosition = t.position;
         t.position = Vector3.zero;
         
         if (!makeSubmeshes)
         {
             meshString.Append("g ").Append(t.name).Append("\n");
         }
         meshString.Append(processTransform(t, makeSubmeshes));
         
         WriteToFile(meshString.ToString(),fileName);
         
         t.position = originalPosition;
         
         End();
         Debug.Log("Exported Mesh: " + fileName);
     }
     
     static string processTransform(Transform t, bool makeSubmeshes)
     {
         StringBuilder meshString = new StringBuilder();
         
         meshString.Append("#" + t.name
                           + "\n#-------" 
                           + "\n");
         
         if (makeSubmeshes)
         {
             meshString.Append("g ").Append(t.name).Append("\n");
         }
         
         MeshFilter mf = t.GetComponent<MeshFilter>();
         if (mf)
         {
             meshString.Append(MeshToString(mf, t));
         }
         
         for(int i = 0; i < t.childCount; i++)
         {
             meshString.Append(processTransform(t.GetChild(i), makeSubmeshes));
         }
         
         return meshString.ToString();
     }
     
     static void WriteToFile(string s, string filename)
     {
         using (StreamWriter sw = new StreamWriter(filename)) 
         {
             sw.Write(s);
         }
     }
 }
 

This is my mesh exporter for android, it is little modified script from this page: http://wiki.unity3d.com/index.php/ExportOBJ