3km is not a very good distance I doubt very much if you would get good coverage on a mountain with these. There are many comments on here about 2 way radios just use the search button to find the info
Was with a group in Italy last year that used the Binatone radios from Argos across the valley and mountains in Livigno without any problems. We also used the Oregon Scientific ones from Argos (Rechargeable) and they were equally as good.
not sure about mountain use. but i've used 2-ways at work and you get what you pay for. As Binatone aren't exactly known for their high quality in this field you might be better trying another. Oregon scientific are good but can be expensive.
Try e-bay as you might be able to find a good deal. Just remember to recharge or change the batteries daily as they don't tend to last too long