I'm looking to purchase 22 i355's for a worksite. I am having difficulty getting a clear answer as to whether or not I can use the phone solely as a walkie talkie. In the past, my company has rented them and what we get is the i355 with direct connect (no group connect, no cell), and a nextel custom unit identification programming with name. Can I just purchase the phones and some used sim cards and just use the phone as a walkie talkie (without paying any kind of a service fee)?