USA it's huge and sparse, but Spain it's the same, it's like USA.rar. Crowded coasts, lots of mountains with a rough interior almost as empty as Lapland modulo Madrid.
So, yes, you can have the issues on phone signal issues.
This is increasingly often the case. Also, don't forget that modern WISP equipment allows for 100Mbps+ speeds for a price next to nothing (Ubiquiti, MikroTik).