L2TP handover can be done with Mikrotik routers.

If you have multiple SIMs, one thing to bear in mind is to use the same hostname on the Control Pages. This will then put the SIMs in different sessions in the same tunnel. Otherwise we see things like:

l2tp,debug tunnel 21 entering state: dead

In the log, indicating that the tunnel for the first SIM has been dropped.

Configuration

The following was taken from: https://www.aa-asterisk.org.uk/Data_sim_L2TP_server_for_ROS

Enable L2TP server on a router board

/interface l2tp-server server
set authentication=pap,chap default-profile=default enabled=yes max-mru=1460 max-mtu=1460 mrru=disabled

Set up an L2TP server

/interface l2tp-server
add comment="L2TP Server" disabled=no name="DATA SIM" user=<this is the number you will see in L2TP debugging, you can also get it from the log on Control Pages related to your data sim>

Add a PPP secret

/ppp secret
add caller-id="" disabled=no limit-bytes-in=0 limit-bytes-out=0 local-address=<IP address on the rb ie 10.10.10.10>\
name=<this is the number you will see in L2TP debugging> \
    password=password profile=default remote-address=<your choice of IP here ie 10.10.10.11> routes="" service=l2tp

The "name" is a number in the format of 4477xxxxxxxx.

You will need to watch the L2TP PPP debug for this, or get it from clueless.