Yes, you can use 오랜만이다 in general situations like when you meet someone in person, talk on the phone, and write email.
For instance, 우리 전화한 지 오랜만이다, which means it's been a while since we talked last time. 우리 마지막으로 이메일한 지 오랜만이다 means it's been a while since we last emailed. 오랜만이다 works just by itself over the phone or in email because the other person will be aware of the situation.