[SalesForce] Journey Builder SMS Send Opt In Behavior

This is as per design - only outbound templates are supported. Refer the official documentation where it states

How to Configure MobileConnect for Use with Journey Builder

Follow the steps below to properly configure your MobileConnect messages for use with Journey Builder:

Contact your Salesforce Marketing Cloud relationship manager to ensure your account allows access to both MobileConnect (using the upgraded version of Contacts) and Journey Builder.

Ensure the MobileConnect Demographic data extension contains the contact data used to personalize any messages used as part of Journey Builder.

Ensure that all contacts you wish to participate in your Journey Builder activities subscribe to the appropriate short or long code and keyword.

You can specify those subscriptions at import or by using messages such as the Mobile Opt-In template.

Create all Outbound MobileConnect messages using the Interaction send method to permit Journey Builder access.

Note that all contacts must initially subscribe to your short or long code and keyword to receive messages at the beginning of the journey. The contacts must also remain subscribed continuously to your short or long code and keyword to continue receving messages as part of the Journey Builder activity. If the contact unsubscribes at any time, that contact will not receive additional messages.

Once you properly configure your MobileConnect messages, those messsages become available for addition to Journey Builder automatically:

Use the Send SMS activity within Journey Builder. Click Configure to select the message you wish to send within that activity. Journey Builder will display a list of all messages using the Interaction send method.

Yes, absolutely you can. I've documented the procedural steps below.

Regarding setting the short/long code and keyword, refer to #10 and #11 of Step 2.

Step 1: Create a MobileConnect List

While Contact Builder enables the creation of Contact Records and configuration of a Contact data model (through linked Attribute Sets), when sending SMS messages from Journey Builder, you still need to create a MobileConnect list; you can't simply use a phone number field from an Event Source Data Extension. In short, any Contacts that are being injected into an Interaction also need to be available within a MobileConnect list if you intend to send them SMS messages using the Send SMS Activity.

1. From the MobileConnect Overview page, select Import File from the Add Contacts menu in the Contacts panel (located in the top right hand corner).
2. Select the 'To a New Standard List' option
3. In the Import Contacts page, don't choose a file to upload, instead, click the Skip Upload » link.
4. Give your list a name in the Save As modal dialog, for example, 'Welcome Program' and leave the format as 'Standard' then click Save

Step 2: Create Import Definition

Next we need to create an Import Definition to Import Contact Data (which is typically from your Event Source Data Extension) into the MobileConnect List you created earlier.

1. From the MobileConnect Overview page, select Import Definitions from the Manage menu in the Contacts panel (located in the top right hand corner).
2. Click the Create button in the top right corner
3. In the Target Destination modal dialog, select the 'Import into a List' option then click OK.
4. In the Reference File panel, select From Existing Data Extension from the menu and browse to the Data Extension containing your mobile subscriber data.
5. In Destination List, select the MobileConnect list that you created earlier, agree to the Opt-in Policy and click Done
6. Click Next
7. Map the fields in your Data Extension to the MobileConnect list. Note that Contact Key, Mobile Number and Locale are required fields. If you don't have a Locale field in your Data Extension, you will need to create one. Refer to the ISO 3166-1 alpha-2 list of country codes.
8. Click Next
9. Enter a name in the Definition Name field
10. Select the short code or long code in the code menu
11. Select the associated keyword in the keyword menu
12. Click Next and Finish

Note: as an alternative to creating a MobileConnect list and setting the Import Definition to import into the list, you can choose to import directly into your 'All Contacts - Mobile' list, depending how you prefer to manage your data.

Step 3: Automate Import

Once you've created your Import Definition, you can schedule the import to run from Automation Studio as part of an Automation by dragging an Import Mobile Contacts Activity to the Automation Canvas and selecting the Import Activity you created earlier.

You would typically run this Activity prior to a Fire Event Activity (when the Contacts are injected into an Interaction).

Finally

Once you've completed all these steps, you're ready to use a Send SMS Activity to send to your target subscribers.