These providers appear to be supported:
Verizon Wireless
AT&T
Sprint (As well as Boost Mobile, Virgin Mobile, Nextel and other related providers)
T-Mobile
Tracfone (And other related providers)
These providers appear to be unsupported:
Cricket Wireless
US Cellular
- pre-paid mobile numbers?
- VOIP carriers?*
- mobile numbers that were previously landline numbers?
- all US-based mobile carriers or just a handful?
* I remember reading that some VOIP carriers are considered mobile carriers.