I like to measure things so I did a test to see how much 12 volt
items we use commonly take.
Battery voltage was at 13.2 volts the float voltage from my PD 4645 converter/charger.
, battery at 80% charge, trying to find signal to make a call, iPhone 4s: 0.47 amps
I expect most "smart phones" to be about the same. Older phones probably less.
MiFi personal hot spot
(net access via Cell system): 0.12 amps
Wilson Sleek cell phone booster
: 0.14 amps
None of these requires a lot of power directly from 12 volts. Now, if you used them with an inverter, and a 120 volt wall wart power supply, the numbers would be considerably higher.
When out camping in a remote area, I typically leave all three of the items above on all the time. The MiFi is in the tow vehicle, so it runs from that battery. The phone and Sleek operate from the Airstream system. I have a 200 watt panel solar system for the Airstream, and maybe 125 watts in the Argosy.