Use Asterisk to open an intercom door

So this might be a weird one.
TL;DR I want asterisk to revive a call and if it’s a specific number wait a few seconds and then send a DTMF tone.

I live in an apartment complex that has an intercom at the front door where guests can call from, this gets routed to a normal phone line and I get a phone call on where I can sent a DTMF tone to open the door.

The landlord will only add one number to the system, since according to him is impossible to add another number which is BS.
Since I live with my SO this can sometimes be a problem, IE when I’m at work.

So I thought this might be the perfect time to start messing around with PBXes.
My idea is to run asterisk on a server and connect a SIM or VoIP line to it, and then when the intercom number calls, I want asterisk to wait a few seconds and then send a DTMF tone. Would this be possible, it there a better way to achieve the same thing?
What do I have to buy? I have figured out that I need a GSM module like a Huawei E155X, but what do I need to connect the RJ11 VoIP line?

I have a regular sim with GSM, VoLTE and VoWifi.
Then I get a hold of a VoIP that terminates at a RJ11 jack, I might be able to get a hold of the SIP account of that line if I’m lucky.

I do realize this is way overkill, but it seems like a fun lite project.

To connect to the RJ11 you would need an Analog Telephone Adapters (ATA) and for the programming I am sure this could be done with Asterisk but I don’t use it enough to know how.

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With Asterisk you can use SendDTMF() [1] to send DTMF

[1] Asterisk 16 Application_SendDTMF - Asterisk Project - Asterisk Project Wiki

Thanks, all I need to know is that it should be possible. Now its time to figure out how.
Also thanks for your fantastic videos!

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