Yes, exactly. 'For a while' would be a good paraphrase. Both 'a while' and 'some time' refer to an unspecified period. We don't know how long this is: all we know is that the two people haven't spoken to each other recently.
Note that 'in' is an informal alternative to 'for' in this context: 'I haven't spoken to you for a while'/'I haven't spoken to you in a while'.