Home phone

If this is a traditional landline (POTS) test at the NID and if bad there report to the phone company, if digital service try resetting the modem. 

Home line busy is either a phone is off the hook or an issue with a jack or inside wiring.

If you have a home security system that uses the phone line, a malfunctioning in that system would also  produce a line busy message.

Well, it can also be a short or ring ground in the plant. 

@spoom2 … true

but before the OP calls and potentially ends up with a $99 service call or higher for an inside issue it is worth noting to check. If have ATT phone, Uverse VOIP check to see if have a flashing PHONE light on front of gateway showing line in use, unplug the cable going into the phone port of the gateway, if flashing stops and light goes solid the issue is inside the home, billable. 

That's why the test from the NID. We don't know until the OP tells us if this is POTS or digital service. 

Hello.  The phone keeps saying home line busy. No one can call and we cannot call out.

Have you tried rebooting the phone or checking the connections? It might help clear up the issue.