can you use a tmobile prepaid sim card on a regular planned cellphone?

Ya sure your t-mobile sim will work in the new phone only if it is unlocked one else if the phone is locked to some other network provider then it wont accept t-mobile sim until you unlock it ...You can easily unlock your phone using sites like Unlocking4Free.com here they are generating network unlock code for some older mobile models at free of cost ...Else if you want to unlock some other new model phone then visit sites like Unlock-Zone.com here they are rendering network unlock code for all mobile models at reliable cost ....After unlocking the phone you can freely use it with any GSM sim ..