diff --git a/app/src/main/kotlin/com/tutpro/baresip/Contact.kt b/app/src/main/kotlin/com/tutpro/baresip/Contact.kt
index aa121ce3..99e8a638 100644
--- a/app/src/main/kotlin/com/tutpro/baresip/Contact.kt
+++ b/app/src/main/kotlin/com/tutpro/baresip/Contact.kt
@@ -76,16 +76,20 @@ sealed class Contact {
         }
 
         fun baresipContact(name: String): BaresipContact? {
-            for (c in BaresipService.baresipContacts.value)
-                if (c.name == name)
-                    return c
+            synchronized(BaresipService.baresipContacts) {
+                for (c in BaresipService.baresipContacts.value)
+                    if (c.name == name)
+                        return c
+            }
             return null
         }
 
         fun androidContact(name: String): AndroidContact? {
-            for (c in BaresipService.androidContacts.value)
-                if (c.name == name)
-                    return c
+            synchronized(BaresipService.androidContacts) {
+                for (c in BaresipService.androidContacts.value)
+                    if (c.name == name)
+                        return c
+            }
             return null
         }
 
@@ -153,7 +157,10 @@ sealed class Contact {
         fun saveBaresipContacts() {
             val avatarFiles = avatarFileNames()
             var contents = ""
-            for (c in BaresipService.baresipContacts.value) {
+            val contacts = synchronized(BaresipService.baresipContacts) {
+                BaresipService.baresipContacts.value.toList()
+            }
+            for (c in contacts) {
                 contents += "\"${c.name}\" <${c.uris.joinToString(",")}>;email=${c.email};id=${c.id}" +
                         ";color=${c.color};favorite=${if (c.favorite) "yes" else "no"}\n"
                 avatarFiles.remove(c.id.toString() + ".png")
@@ -281,13 +288,21 @@ sealed class Contact {
 
         fun contactsUpdate() {
             val newContacts = mutableListOf<Contact>()
-            if (BaresipService.contactsMode != "android")
-                for (c in BaresipService.baresipContacts.value)
+            if (BaresipService.contactsMode != "android") {
+                val baresipContacts = synchronized(BaresipService.baresipContacts) {
+                    BaresipService.baresipContacts.value.toList()
+                }
+                for (c in baresipContacts)
                     newContacts.add(c.copy())
-            if (BaresipService.contactsMode != "baresip")
-                for (c in BaresipService.androidContacts.value)
+            }
+            if (BaresipService.contactsMode != "baresip") {
+                val androidContacts = synchronized(BaresipService.androidContacts) {
+                    BaresipService.androidContacts.value.toList()
+                }
+                for (c in androidContacts)
                     if (!nameExists(c.name, newContacts, true))
                         newContacts.add(c.copy())
+            }
             newContacts.sortBy {
                 when (it) {
                     is BaresipContact -> if (it.favorite) "0" + it.name else "1" + it.name
@@ -299,24 +314,30 @@ sealed class Contact {
         }
 
         fun addBaresipContact(contact: BaresipContact) {
-            BaresipService.baresipContacts.value += contact
+            synchronized(BaresipService.baresipContacts) {
+                BaresipService.baresipContacts.value += contact
+            }
             saveBaresipContacts()
             contactsUpdate()
         }
 
         fun updateBaresipContact(id: Long, contact: BaresipContact) {
-            val updatedContacts = BaresipService.baresipContacts.value.toMutableList()
-            updatedContacts.removeIf { it.id == id }
-            updatedContacts.add(contact)
-            BaresipService.baresipContacts.value = updatedContacts.toList()
+            synchronized(BaresipService.baresipContacts) {
+                val updatedContacts = BaresipService.baresipContacts.value.toMutableList()
+                updatedContacts.removeIf { it.id == id }
+                updatedContacts.add(contact)
+                BaresipService.baresipContacts.value = updatedContacts.toList()
+            }
             saveBaresipContacts()
             contactsUpdate()
         }
 
         fun removeBaresipContact(contact: BaresipContact) {
-            val removed = BaresipService.baresipContacts.value.toMutableList()
-            removed.removeIf { it.id == contact.id }
-            BaresipService.baresipContacts.value = removed.toList()
+            synchronized(BaresipService.baresipContacts) {
+                val removed = BaresipService.baresipContacts.value.toMutableList()
+                removed.removeIf { it.id == contact.id }
+                BaresipService.baresipContacts.value = removed.toList()
+            }
             saveBaresipContacts()
             contactsUpdate()
         }
diff --git a/app/src/main/kotlin/com/tutpro/baresip/UserAgent.kt b/app/src/main/kotlin/com/tutpro/baresip/UserAgent.kt
index 2a217436..d0d3a201 100644
--- a/app/src/main/kotlin/com/tutpro/baresip/UserAgent.kt
+++ b/app/src/main/kotlin/com/tutpro/baresip/UserAgent.kt
@@ -16,22 +16,28 @@ class UserAgent(val uap: Long, virtualAccount: Account? = null) {
     }
 
     fun add() {
-        val updatedUas = uas.value.toMutableList()
-        updatedUas.add(this)
-        uas.value = updatedUas.toList()
-        uasStatus.value = statusMap()
+        synchronized(uas) {
+            val updatedUas = uas.value.toMutableList()
+            updatedUas.add(this)
+            uas.value = updatedUas.toList()
+            uasStatus.value = statusMap()
+        }
     }
 
     fun remove() {
-        val updatedUas = uas.value.toMutableList()
-        updatedUas.remove(this)
-        uas.value = updatedUas.toList()
-        uasStatus.value = statusMap()
+        synchronized(uas) {
+            val updatedUas = uas.value.toMutableList()
+            updatedUas.remove(this)
+            uas.value = updatedUas.toList()
+            uasStatus.value = statusMap()
+        }
     }
 
     fun updateStatus(status: Int) {
-        uas.value.find { it.uap == this.uap }?.status = status
-        uasStatus.value = statusMap()
+        synchronized(uas) {
+            uas.value.find { it.uap == this.uap }?.status = status
+            uasStatus.value = statusMap()
+        }
     }
 
     fun calls(dir: String = ""): ArrayList<Call> {
@@ -62,12 +68,14 @@ class UserAgent(val uap: Long, virtualAccount: Account? = null) {
     }
 
     fun makeDefault() {
-        val index = uas.value.indexOf(this)
-        val updatedUas = uas.value.toMutableList()
-        updatedUas.removeAt(index)
-        updatedUas.add(0, this)
-        uas.value = updatedUas.toList()
-        uasStatus.value = statusMap()
+        synchronized(uas) {
+            val index = uas.value.indexOf(this)
+            val updatedUas = uas.value.toMutableList()
+            updatedUas.removeAt(index)
+            updatedUas.add(0, this)
+            uas.value = updatedUas.toList()
+            uasStatus.value = statusMap()
+        }
     }
 
     companion object {
@@ -114,25 +122,27 @@ class UserAgent(val uap: Long, virtualAccount: Account? = null) {
         }
 
         fun updateColorblindStatus() {
-            val updatedUas = uas.value.toMutableList()
-            for (ua in updatedUas)
-                ua.status =
-                    if (colorblind)
-                        when (ua.status) {
-                            R.drawable.circle_green -> R.drawable.circle_green_blind
-                            R.drawable.circle_yellow -> R.drawable.circle_yellow_blind
-                            R.drawable.circle_red -> R.drawable.circle_red_blind
-                            else -> R.drawable.circle_white
-                        }
-                    else
-                        when (ua.status) {
-                            R.drawable.circle_green_blind -> R.drawable.circle_green
-                            R.drawable.circle_yellow_blind -> R.drawable.circle_yellow
-                            R.drawable.circle_red_blind -> R.drawable.circle_red
-                            else -> R.drawable.circle_white
-                        }
-            uas.value = updatedUas.toList()
-            uasStatus.value = statusMap()
+            synchronized(uas) {
+                val updatedUas = uas.value.toMutableList()
+                for (ua in updatedUas)
+                    ua.status =
+                        if (colorblind)
+                            when (ua.status) {
+                                R.drawable.circle_green -> R.drawable.circle_green_blind
+                                R.drawable.circle_yellow -> R.drawable.circle_yellow_blind
+                                R.drawable.circle_red -> R.drawable.circle_red_blind
+                                else -> R.drawable.circle_white
+                            }
+                        else
+                            when (ua.status) {
+                                R.drawable.circle_green_blind -> R.drawable.circle_green
+                                R.drawable.circle_yellow_blind -> R.drawable.circle_yellow
+                                R.drawable.circle_red_blind -> R.drawable.circle_red
+                                else -> R.drawable.circle_white
+                            }
+                uas.value = updatedUas.toList()
+                uasStatus.value = statusMap()
+            }
         }
 
         fun statusMap(): Map<String, Int> {