Another possible provider is
sipgate.co.uk. Set up and DID is free , no charges to you for incoming calls. They have geographic UK numbers across the UK, so it should be possible to get one local to your mother in law, so calls to it for her will only be charged at local rate.
The one complication is that to get a
sipgate.co.uk geographic number, you have to be resident in the UK. You would have to get your mother in law to register the number. After that the number can be used anywhere in the world. Their web site even advertises that as a benefit to users.
I've been using them here in the UK for incoming and some outgoing calls for several years - quality and reliability seem good. Anyhow there's no costs involved in trying!
