> Has the security of the basic phone call changed much, in the last 10 years ?
>
> So, do smartphones utilise anything new [purely in] the initiation and connection of just the phone call itself ?

Yes. There are new technologies used to establish phone calls in cellular networks. Those new technologies mitigate some attacks which were possible due to flaws in the older ones. So if you use a "dumbphone" that runs on the older technologies you are subject to those attacks (i.e. the inverse is true, the smartphone is in this respect more secure).   

The technologies used in the cellular networks basically evolved over time like this: 1st generation (analogue), 2nd generation (GSM etc.), 3rd generation (UMTS etc.), 4th generation (LTE etc.).

If you use a device running for example the GSM technology, an attacker might intercept your calls with hardware costs of [only about $30 USD][1]. Intercepting calls made with the newer technologies is harder up to a point where only nation state attackers can perform them.

[1]: http://hackaday.com/2013/10/22/cracking-gsm-with-rtl-sdr-for-thirty-dollars/