The Nokia 6 lacks support for 700MHz Band 28, which means that the phone's data speeds as well as the coverage both indoor and outdoors aren't as optimal as they could have been for regions that do support it or plan to support it in the future. Having 700MHz support also feels the gap and allows us to use 4G in places where there is not a good reception for the higher frequencies, and where that without 700MHz, the connection will just drop to 3G. If you intended to use the phone in 4G LTE supported area, this is probably important. Without band 28, you will only access a smaller subset of the network infrastructure, so the realization of the bandwidth that is achievable won't be used to its fullest
Here is a very informative video by amaysim that talks about the 700MHz and its benefits:
The Nokia 6 is now available also in the Philippines. If you are a SMART or Globe provider, you might already know that those two carriers do support 700MHz for 4G (LTE). It's important to note that not all areas have 700MHz Band support. This Band brings an improved data transfer speed and better signal reception, even indoors, and this is why it's favorable among phone users. This band is supposed the answer the great demand for providing faster Internet services.
This is why some reviewers who reviewed the Nokia 6 were disappointed to see that there is not support for 700MHz Band 28, which has high demand in the Philippines. Keep in mind that this is referred to the 4G LTE network, not Wi-Fi. For the Wi-Fi, the Nokia 6 does have dual-band Wi-Fi, so you can enjoy a large bandwidth and download at increased speed.
Of course the reason the Nokia 6 doesn't support Band 28 is because it was made for the Chinese market, not for intentional markets. If you look at the Xiaomi Mi Mix that is a phone that was designed for Globa LTE support, you can see that B28 LTE appears in the list, among many other bands. But the Mi Mix is designed from the ground up with a huge LTE support. The Nokia 6 wasn't designed for that and therefore there is no need to implement more antennas and a wider Band support if the phone itself is meant to be marketed only for specific countries. I've read that the Nokia 6 isn't officially released in the Philippines, although some say that it is. I think that even through it found its way there, Nokia plans was to market it for the China region only, and I remember that being mentioned in the official press releases if I'm not wrong.
For many people not having a 700MHz can even be a deal breaker and people won't buy a phone without support for this specific band. Many countries in the Asian pacific region and south America already adopted the APT segmentation scheme, including Australia, India, Thailand, Vietnam, Mexico and others. From what I've read on Wikipedia, there is also plan to bring the 700MHz to European countries, but there were some difficulties due to that band being used in digital terrestrial television services. In the US there is not plan to make changes to support this band.
So 700 MHz will me mostly used in Asia pacific countries and continue to be allocated in more regions in the future. We can see that in the present, most mobile devices do not offer an RF design that support a wide range of LTE bands, in the future many will.
If you live in the Philippines, you can buy the Nokia 6 from lazada.com.ph website, although the last time I've checked it was sold out. I mentioned the Philippines because this was brought up in many places on the web, but this is a disadvantage for those of you who live in areas that has Band 28 support and want a phone that does have a support for it. It might be better to wait for future Nokia phones in 2017 that night have 700 MHz support and skip the Nokia 6.
There are obviously tons of phones that do support 4G LTE Band 28, 700Mhz, including the Galaxy J7, iPhone 6 Plus, HTC 10, , LG G5, Asus Zenfone 3, Oppo F1S, Sony Xperia XZ, iPhone 7, Samsung Galaxy Note 5 and many many others.
This is obviously not a significant disadvantage if at all if you live in areas that don't support it or you won't needed it anyway, but I thought it's was important to mention it for those who do plan to buy the Nokia 6 and had B28 support as part of their must-have features.