Making phone calls in Montenegro

I do not have a local landline.
Most of my friends don't have either. Everyone just use mobile phones.

If you need to call other countries a lot, the best solution is a hardware VoIP phone   some SIP subscription. Buy a hardware like this http://www.gigaset.com/hq_en/telephones … 30-ip.html Connect the base station to you home router with an Ethernet cable. Subscribe to any VoIP operator[s] you like (the gigaset supports several parallel accounts), e.g. when I've been calling US a lot I've been using http://www.sipdiscount.com And if you need a phone # for incoming calls, rent one in any country you like, e.g. https://www.didww.com/

For the mobile, I recommend getting a prepaid SIM card from http://telekom.me = T-Mobile.
Make sure you're buying an ordinary prepaid card, not that special Tourist offer (the tourists card have severe limitations you don't want).
You'll be asked for an ID, show them any document with your photo like a passport or driving license.
If you need mobile internet, it'll cost you €4-€5 per 1GB data for 15 days, you can activate those packages through SMS (“mo int15” to number 1477, €5) or USSD (€4, *111# then navigate through menu, Moja opcia / Internet opcije / 15 dana).