Plugged in or out

I've never had a telephone in a RV....
Presume you mean electrical plug in, aka shore power as it's sometimes called. Depends. But yes more often than not, it's plugged in.
Caution, if you have a cheap converter, it could overcharge the batteries if left plugged in indefinitely.

Plugged in.

The battery chargers in modern power converters are perfectly capable of maintaining the house batteries in a fully-charged state.

After the batteries become fully charged, the amount of AC power consumed by the converter is negligible - not nearly enough to notice on your electric bill.

Bfrnk wrote:
Do you keep your rv plug into landline when at home and not on the road?

No.

Converters are not always optimized for battery charging.

I do have a modest solar installation to keep the batteries (generator, chassis and house) in tip top condition.

Bfrnk wrote:
Do you keep your rv plug into landline when at home and not on the road?

I did. but then I also used it every day (My Ham Shack)

I did, however. Notice a major jump in my power bill.

Always plugged in whether in storage or RV park for 14 years and no problem.

We do as well, we use our rig so frequently that we are fully charged and fridge is always at operating temps for quick getaways. We have smart converters and inverter chargers that incorporate multiphase charging routines to keep our 12 volt reserves happy and healthy, average 8 years with our golfcart batteries before replacement.

plugged in 24/7 365.
The only time my RV is unplugged is when it is traveling down the road.

I do keep it plugged in, although I disconnect the battery (connect it for a day once a month to keep it charged). I do this because the humidity here is high all year around, and I keep a dehumidifier running in it to keep mold down. I also, from time to time, need to run the refrigerator for "special events." And every so often we have guests.

Plugged in with dehumidifier on but with converter breaker off.
Solar charger connected to battery with negative wire disconnected.

Plugged in with heat pump on in winter and A/C on in summer. Make numerous trips thru-out the year. Never have to winterize. On a trip currently in mountains with lows in 20s at night.