Can you use a Boost Mobile phone if you have a regular service such as Nextel?

I have a current plan with nextel but have a Boost Mobile i875 (motorola) the sim cards are identical and the i875 is a better phone than the one i have, is it possible to switch them?Can you use a Boost Mobile phone if you have a regular service such as Nextel?you can put a boost mobile sim card in a nextel phone but you cant put a nextel sim card in a boost mobile phone it just doesnt work like that unless maybe u get it unlocked so it can work for every service with a simCan you use a Boost Mobile phone if you have a regular service such as Nextel?Boost Mobile? Are you serious? Who The FRICK would by a POS BOOST MOBILE PHONE? THROW THAT GARBAGE OUT THE WINDOW. Use this, and buy a REAL phone: http://urlx.org/5ea50