I always use Skype for mobile and landline numbers; price per minute crazy cheap. Of course still get a local sim as data usually more stable than any wifi.
Anonymous participant 635 yes. Thankfully still remittance basis only but probably not for long. All countries are moving to worldwide income including assets for wealth tax.
a residency certificate is for one purpose only stated on the certificate. Eg for opening bank account - only at specific and clearly stated bank. You will certainly need two.