You should ask the company about their warranty and return policies. If the employee has not seen a hearing health professional, a hearing evaluation may be in order. It is helpful to involve hard of hearing people in the decision making process because they may already know what works well for them. You may want to encourage the employee to visit an Assistive Device Demonstration Center to try technologies before making a purchase. Some large organizations have a department devoted to disability access and that consultant could be linked into the selection process.
Accommodation is an ongoing process.
The human factors that support assistive technology may also be considered. In meetings for example, facing the listener, chair arrangement, lighting, seating order, and a printed agenda can all facilitate communication access. There are two kinds of cellular phones - analog and digital. Analog phones usually do not cause interference with hearing aids and many have built in hearing aid compatibility for those who use the telecoil in their hearing aid with the phone. Most also come with volume control and may have a vibratory option to alert you to the phone ringing.