Smartphone or satnav?

I currently do not own a smartphone, I have never found the need to take on the added expense. However I have recently got a car and decided that I would need a satnav or a satnav app.

I'm in the UK, I would need the functionality of speed camera checks and live traffic updates. Due to work I travel fairly extensively sometimes in rural areas.

My question is, will a smartphone app be able to maintain coverage throughout most of the UK or am I better off getting a dedicated satnav?