Why can you not use VoIP calls either?

Before giving the answer to this question, you need to know whether you are looking for cellular calls as well as internet-based (VoIP) calls. Voice or video calling is not possible on United Airlines flights, no matter what is your aircraft type or Wi-Fi service you are using. Here are the rules and explanations about what is allowed and what is not. However, calls are not specifically banned by the policy defined by the air management, but rather by FCC regulation. When the airplane is flying at high speed, it flies through the gap between the ground-based cell towers quicker than the networks can process handoffs, resulting in interference. The limitation is not unique to United, but has been around for decades before the advent of Wi-Fi on the plane. Your concern can I make a phone call on United Airlines cannot be fixed on any flight (domestic or international) on any U.S. carrier.

Web browsing
Email
Text-based messaging apps
Online video and music streaming (headphones must be provided as per United's contract of carriage)
Bandwidth permitting, file downloads are possible and cloud syncing is possible.

Does this depend on bandwidth?

Bandwidth is more than adequate for voice and video calling, especially on Starlink-equipped aircraft. It is a policy and not a technical issue. The restriction is put in place to minimise disruption in the cabin where there is no opportunity for passengers not to hear calls in neighbouring seats, United has said. Other carriers, such as Delta, have similar policies and flight attendant unions have been pushing for such industry-wide restrictions for several years, pointing to a perennial problem with passenger conflict.

Reasons to call on United Airlines

To modify any existing reservation
To book a new flight
To check gate changes, flight schedules, or travel advisories
To check refund eligibility or cancel a trip
To pay for baggage fees, add baggage, or report damaged luggage
To request medical assistance inside the flight
To file a complaint about flight delay
To redeem travel credits, vouchers, or flight certificates
To report booking errors or payment problems
To request a seat upgrade to extra legroom seat
To access special benefits and discount offers
To collect information about in-flight shopping and entertainment options

Will this be different in the future?

This policy is not likely to be changed in the near future. The restriction is not technical so it is not expected that any improvements in connectivity speed on board will impact it. If there was any future change, it would be a public policy change from United and not a network change. On all aircraft, both cell phone and Wi-Fi calls are not available on United Airlines when asked, "Can I make a phone call on United Airlines?” Cell phone, email and streaming are available throughout the flight.