diff --git a/native/account/registration/avatar-selection.react.js b/native/account/registration/avatar-selection.react.js
--- a/native/account/registration/avatar-selection.react.js
+++ b/native/account/registration/avatar-selection.react.js
@@ -8,6 +8,7 @@
 import RegistrationButton from './registration-button.react.js';
 import RegistrationContainer from './registration-container.react.js';
 import RegistrationContentContainer from './registration-content-container.react.js';
+import { RegistrationContext } from './registration-context.js';
 import type { RegistrationNavigationProp } from './registration-navigator.react.js';
 import type {
   CoolOrNerdMode,
@@ -88,7 +89,13 @@
     [],
   );
 
+  const [registrationInProgress, setRegistrationInProgress] =
+    React.useState(false);
+
   React.useEffect(() => {
+    if (registrationInProgress) {
+      return undefined;
+    }
     setRegistrationMode({
       registrationMode: 'on',
       successCallback: setClientAvatarFromSelection,
@@ -96,9 +103,27 @@
     return () => {
       setRegistrationMode({ registrationMode: 'off' });
     };
-  }, [setRegistrationMode, setClientAvatarFromSelection]);
+  }, [
+    registrationInProgress,
+    setRegistrationMode,
+    setClientAvatarFromSelection,
+  ]);
+
+  const registrationContext = React.useContext(RegistrationContext);
+  invariant(registrationContext, 'registrationContext should be set');
+  const { register } = registrationContext;
 
-  const onProceed = React.useCallback(() => {}, []);
+  const onProceed = React.useCallback(async () => {
+    setRegistrationInProgress(true);
+    try {
+      await register({
+        ...userSelections,
+        avatarData,
+      });
+    } finally {
+      setRegistrationInProgress(false);
+    }
+  }, [register, userSelections, avatarData]);
 
   const clientAvatar = avatarData?.clientAvatar;
   const userInfoOverride = React.useMemo(
@@ -118,7 +143,7 @@
           <View style={styles.editUserAvatar}>
             <EditUserAvatar
               userInfo={userInfoOverride}
-              disabled={false}
+              disabled={registrationInProgress}
               prefetchedAvatarURI={prefetchedAvatarURI}
             />
           </View>
@@ -128,7 +153,7 @@
         <RegistrationButton
           onPress={onProceed}
           label="Submit"
-          variant="disabled"
+          variant={registrationInProgress ? 'loading' : 'enabled'}
         />
       </RegistrationButtonContainer>
     </RegistrationContainer>
diff --git a/native/account/registration/registration-context-provider.react.js b/native/account/registration/registration-context-provider.react.js
--- a/native/account/registration/registration-context-provider.react.js
+++ b/native/account/registration/registration-context-provider.react.js
@@ -3,12 +3,20 @@
 import * as React from 'react';
 
 import { RegistrationContext } from './registration-context.js';
+import { useRegistrationServerCall } from './registration-server-call.js';
 
 type Props = {
   +children: React.Node,
 };
 function RegistrationContextProvider(props: Props): React.Node {
-  const contextValue = React.useMemo(() => ({}), []);
+  const registrationServerCall = useRegistrationServerCall();
+  const contextValue = React.useMemo(
+    () => ({
+      register: registrationServerCall,
+    }),
+    [registrationServerCall],
+  );
+
   return (
     <RegistrationContext.Provider value={contextValue}>
       {props.children}
diff --git a/native/account/registration/registration-context.js b/native/account/registration/registration-context.js
--- a/native/account/registration/registration-context.js
+++ b/native/account/registration/registration-context.js
@@ -2,7 +2,11 @@
 
 import * as React from 'react';
 
-export type RegistrationContextType = {};
+import type { RegistrationServerCallInput } from './registration-types.js';
+
+export type RegistrationContextType = {
+  +register: RegistrationServerCallInput => Promise<void>,
+};
 
 const RegistrationContext: React.Context<?RegistrationContextType> =
   React.createContext<?RegistrationContextType>();
diff --git a/native/account/registration/registration-server-call.js b/native/account/registration/registration-server-call.js
new file mode 100644
--- /dev/null
+++ b/native/account/registration/registration-server-call.js
@@ -0,0 +1,118 @@
+// @flow
+
+import * as React from 'react';
+import { Alert, Platform } from 'react-native';
+import { useDispatch } from 'react-redux';
+
+import { setDataLoadedActionType } from 'lib/actions/client-db-store-actions.js';
+import { registerActionTypes, register } from 'lib/actions/user-actions.js';
+import type { LogInStartingPayload } from 'lib/types/account-types.js';
+import {
+  useServerCall,
+  useDispatchActionPromise,
+} from 'lib/utils/action-utils.js';
+
+import type {
+  RegistrationServerCallInput,
+  UsernameAccountSelection,
+} from './registration-types.js';
+import { NavContext } from '../../navigation/navigation-context.js';
+import { useSelector } from '../../redux/redux-utils.js';
+import { nativeLogInExtraInfoSelector } from '../../selectors/account-selectors.js';
+import { setNativeCredentials } from '../native-credentials.js';
+import { useSIWEServerCall } from '../siwe-hooks.js';
+
+function useRegistrationServerCall(): RegistrationServerCallInput => Promise<void> {
+  const navContext = React.useContext(NavContext);
+  const logInExtraInfo = useSelector(state =>
+    nativeLogInExtraInfoSelector({
+      redux: state,
+      navContext,
+    }),
+  );
+
+  const dispatchActionPromise = useDispatchActionPromise();
+  const callRegister = useServerCall(register);
+
+  const registerUsernameAccount = React.useCallback(
+    async (accountSelection: UsernameAccountSelection) => {
+      const extraInfo = await logInExtraInfo();
+      const registerPromise = (async () => {
+        try {
+          const result = await callRegister({
+            ...extraInfo,
+            username: accountSelection.username,
+            password: accountSelection.password,
+          });
+          await setNativeCredentials({
+            username: result.currentUserInfo.username,
+            password: accountSelection.password,
+          });
+          return result;
+        } catch (e) {
+          if (e.message === 'username_reserved') {
+            Alert.alert(
+              'Username reserved',
+              'This username is currently reserved. Please contact support@' +
+                'comm.app if you would like to claim this account.',
+            );
+          } else if (e.message === 'username_taken') {
+            Alert.alert(
+              'Username taken',
+              'An account with that username already exists',
+            );
+          } else if (e.message === 'client_version_unsupported') {
+            const app = Platform.select({
+              ios: 'App Store',
+              android: 'Play Store',
+            });
+            Alert.alert(
+              'App out of date',
+              'Your app version is pretty old, and the server doesn’t know how ' +
+                `to speak to it anymore. Please use the ${app} app to update!`,
+            );
+          } else {
+            Alert.alert('Unknown error', 'Uhh... try again?');
+          }
+          throw e;
+        }
+      })();
+      dispatchActionPromise(
+        registerActionTypes,
+        registerPromise,
+        undefined,
+        ({ calendarQuery: extraInfo.calendarQuery }: LogInStartingPayload),
+      );
+      await registerPromise;
+    },
+    [logInExtraInfo, callRegister, dispatchActionPromise],
+  );
+
+  const siweServerCallParams = React.useMemo(() => {
+    const onServerCallFailure = () => {
+      Alert.alert('Unknown error', 'Uhh... try again?');
+    };
+    return { onFailure: onServerCallFailure };
+  }, []);
+  const siweServerCall = useSIWEServerCall(siweServerCallParams);
+
+  const dispatch = useDispatch();
+  return React.useCallback(
+    async (input: RegistrationServerCallInput) => {
+      if (input.accountSelection.accountType === 'username') {
+        await registerUsernameAccount(input.accountSelection);
+      } else {
+        await siweServerCall(input.accountSelection);
+      }
+      dispatch({
+        type: setDataLoadedActionType,
+        payload: {
+          dataLoaded: true,
+        },
+      });
+    },
+    [registerUsernameAccount, siweServerCall, dispatch],
+  );
+}
+
+export { useRegistrationServerCall };
diff --git a/native/account/registration/registration-types.js b/native/account/registration/registration-types.js
--- a/native/account/registration/registration-types.js
+++ b/native/account/registration/registration-types.js
@@ -36,3 +36,10 @@
       +updateUserAvatarRequest: UpdateUserAvatarRequest,
       +clientAvatar: ClientAvatar,
     };
+
+export type RegistrationServerCallInput = {
+  +coolOrNerdMode: CoolOrNerdMode,
+  +keyserverUsername: string,
+  +accountSelection: AccountSelection,
+  +avatarData: ?AvatarData,
+};