Who I have the same questioned this topic

My daughter is traveling to Swaziland this summer.  We are planning to get her an I phone 4-s as her I phone 4 does not dial internationally.  She will have access to WI-FI and will use this for the majority of her communication however, we would like her to be able to dial as necessary.  My questions are as follows:

1.  How can we be sure she has the roaming turned off while she is about to not incur large expense?  Does she keep it in airplane mode unless she is in the wi-fi area?

2.  Is the I phone 4-S a good selection for this?

3.  Any other advice is appreciated.

Thanks,

David