Nice to see the modern thinkers are on-line
What makes you think they forgot?
Let's look at the history: first we had analogue mobile, which allowed people to make phone calls without a wire; then we got GSM which meant that we could actually make calls in a consistent way around the world (and had a bit more security than analogue). Then along came 3G to provide 'true data capability', but instead was used mostly for voice until we got decent rates with HSPA 5 years later.
So, today we have GSM with 99% coverage for VOICE, 3G with 60-80% VOICE coverage (depending on how you look at it), and 3G with 60% or less DATA coverage. Now mobile operators are facing a big challenge on DATA, since people realised they can and want to stream pr0n in their bedrooms on their mobiles. And the problem is only going to get worse (the data challenge, not the pr0n).
Enter LTE, whose biggest feature is the chance to have **up to** greater than 100 Mbps in a cell (no-one ever talks about voice capacity in LTE)
So the reality is
- you have nearly 100% voice coverage already (on well proven, robust and long ago paid for hardware)
- voice capacity is not a problem on >90% of the existing network
- you've got a major data challenge around the corner.
a) invest in a high-speed, high-capacity data only overlay network and slowly replace your trusted voice network once you have sufficient coverage and confidence, or
b) invest today a few billion extra to install a new IP-based voice network that isn't needed and still won't give you near 80% population coverage for over 5 years?
Most early observers and stakeholders have considered the first option the best, so LTE was designed to be a data network in the first instance, with an upgrade path to IP voice. It's not that anybody forgot, it's just not needed now.
p.s. you can always use a VoIP client (e.g. Skype) on top of the data only network if it really matters that much to you.
p.p.s. Have you seen the LTE terminals on offer today and near future? Not really pocket sized unless you have very big pockets (except for the USB sticks, and they don't have a keypad, speaker or screen).