The ability to add multiple phone numbers for different people, which can be used as an extension of your business (aside from being able to make calls) or even just personal use so you don’t have to carry around more than one number in case it gets lost/stolen etc.
Also they are generally cheap enough that I feel comfortable using them with clients/customers all over London without having expensive bills come through my account each month! Some features could do better like not requiring authentication every time i try access voicemails but other then this the app is great if looking at something reasonably priced where calling isn't too much work compared to paying monthly charges elsewhere. We needed somewhere we had our own mobile number separate form main office line, also allowing us call customers across london easily via their gps location data - voogie was perfect solution here.