The simplest way is DISA with asterisk: you call your landline number and asterisk transfers your call to DISA, there you need to type in 6(or more)-digit pin code(or no pin at your own risk!), afterwards, you get a dialtone and you can dial out as you were at home.
Callback can be implemented with either OBI-ATA or asterisk. PLZ check old post in this forum.