D702i is Mitsubishi and doesn't have roaming. And NTT DoCoMo's Japanese FOMA models cannot be unlocked (LG & Motorola can be in some situations, the bigger Japanese models cannot be).
And so that you know:
In the model names xXXXiY (x being a letter and X being the number of the lineup with the Y being a bonus letter either meaning some special function [X for HSDPA] or new lineup [like the X902iS] ) the makers go like following - D (Mitsubishi), P (Panasonic), N (NEC), SH (Sharp), M (Motorola), F (Fujitsu), SA (Sanyo), SO (SonyEricsson), L (LG).
For example:
D903i is a
Mitsubishi made 903i model
N902iS is a
NEC 902iS series model
P903i
X is a
Panasonic HSDPA 903i series model
SH903i is a
Sharp 903i series model
I hope this makes the NTT DoCoMo naming scheme easier to understand
. SoftBank Mobile, on the other hand uses the opposite naming scheme, having no "series", but just a number and the maker's letters - like in 904SH where the SH means Sharp and goes
after the number. I say this because I know some people still talk about SoftBank models with the letters before the numbers - which is the scheme for NTT DoCoMo phones.