We have an Ooma Telo and 10 MB DSL at our camper.
I did my research, although more than a few seasonal folks up there have MagicJacks, I found their customer service to be a little less than helpful. Ooma on the other hand has been great.
I plug in our cordless phone to the Ooma and then use two other bases so we have a phone outside most times.
We signed up for the premium ($10/month) so we can call forward to cell phones and do call blocking. We ported the number from our landline. But $4/month for a telephone beats the heck out of the landline that I paid $35+ taxes for. Oh, and it's lasted through one of the coldest winters we have had last year, in an insulated Minnesota room.
There are other companies who do voice over ip phones too.