Digital frequency phones don't cause any issue, except POSSIBLY the Moto IDEN network(nextel) phones with the PTT they did have some legit interference issues but it was mostly on emergency frequency used by rural fire dept and emergency services.

They are totally different than any GSM or CDMA phone from other carriers(or sprint CDMA) and also have a very limited life as the FCC is forcing them off that band due to these issues.