It wouldn't take much for me to switch, although with my limited mobile usage I'm not exactly an ideal customer. I'd be looking for things like (sort of order)
- prepay or < $5/month on account
- boring old 900MHz GSM for device selection and battery life
- customer service, my preference being via email/online
- prices similar to or less than Vodafone's old Motormouth prepay, def no more than 20c/text not so worried about calls
- Easy access to an itemised bill online, bonus points for simple HTTP(S) GETable CSV or XML download
- Extra bonus points for coverage at Lake Tekapo motor camp and main bay (perhaps some little pico cells or something). Vodafone coverage stops dead 100m away
- Lots of geek points if you can easily setup your own personal short call codes that dial a SIP URI and are charged at hardly NZ mobile like rates
- Data with reasonable charges (eg vodafones $1/day) and either data packs or really cheap right from the first byte
- At least Some 3G, 2100MHz is what my current 3G devices are capable of
- International roaming (calls,txt and data) with non-crazy charges, at the very least with Aussie
- I guess if I ever started really using my mobile for contacting people then TXT packs and/or bestmate like addons would be of interest
Basically as long as they aren't worse than Vodafone I'd seriously consider switching, esp with easy access to an itemised bill.